Simplify Configure in a few ways

 - No need to distinguish between gcc-llvm and clang. First of all,
   gcc-llvm is quite old and surely unmaintained by now. Second of all,
   none of the code actually care about that distinction!

   Now, it does make sense to consider C multiple frontends for LLVMs in
   the form of clang vs clang-cl (same clang, yes, but tweaked
   interface). But this is better handled in terms of "gccish vs
   mvscish" and "is LLVM", yielding 4 combinations. Therefore, I don't
   think it is useful saving the existing code for that.

 - Get the remaining CC_LLVM_BACKEND, and also TABLES_NEXT_TO_CODE in
   mk/config.h the normal way, rather than hacking it post-hoc. No point
   keeping these special cases around for now reason.

 - Get rid of hand-rolled `die` function and just use `AC_MSG_ERROR`.

 - Abstract check + flag override for unregisterised and tables next to
   code.

Oh, and as part of the above I also renamed/combined some variables
where it felt appropriate.

 - GccIsClang -> CcLlvmBackend. This is for `AC_SUBST`, like the other
 Camal case ones. It was never about gcc-llvm, or Apple's renamed clang,
 to be clear.

 - llvm_CC_FLAVOR -> CC_LLVM_BACKEND. This is for `AC_DEFINE`, like the
 other all-caps snake case ones. llvm_CC_FLAVOR was just silly
 indirection *and* an odd name to boot.

19 files changed, 101 insertions, 115 deletions

diff --git a/aclocal.m4 b/aclocal.m4
index 2072a33b36..1218203bfc 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -842,6 +842,48 @@ AC_DEFUN([FP_CHECK_SIZEOF_AND_ALIGNMENT],
 FP_CHECK_ALIGNMENT([$1])
 ])# FP_CHECK_SIZEOF_AND_ALIGNMENT
 
+# FP_DEFAULT_CHOICE_OVERRIDE_CHECK(
+#   flag, name, anti name, var name, help string,
+#   [var true val], [var false val], [flag true val])
+# ---------------------------------------------------
+# Helper for when there is a automatic detection and an explicit flag for the
+# user to override disable a feature, but not override enable a feature.
+#
+# $1 = flag of feature
+# $2 = name of feature
+# $3 = name of anti feature
+# $4 = name of variable
+# $5 = help string
+# $6 = when true
+# $7 = when false
+# $8 = default explicit case (yes/no). Used for handle "backwards" legacy
+#      options where enabling makes fewer assumptions than disabling.
+AC_DEFUN(
+    [FP_DEFAULT_CHOICE_OVERRIDE_CHECK],
+    [AC_ARG_ENABLE(
+        [$1],
+        [AC_HELP_STRING(
+            [--enable-$1],
+            [$5])],
+        [AS_IF(
+           [test x"$enableval" = x"m4_default([$8],yes)"],
+           [AS_CASE(
+               [x"$$4Default"],
+               [x"m4_default([$6],YES)"],
+                 [AC_MSG_NOTICE([user chose $2 matching default for platform])],
+               [x"m4_default([$7],NO)"],
+                 [AC_MSG_ERROR([user chose $2 overriding only supported option for platform])],
+               [AC_MSG_ERROR([invalid default])])
+            $4=m4_default([$6],YES)],
+           [AS_CASE(
+               [x"$$4Default"],
+               [x"m4_default([$6],YES)"],
+                 [AC_MSG_NOTICE([user chose $3 overriding for platform])],
+               [x"m4_default([$7],NO)"],
+                 [AC_MSG_NOTICE([user chose $3 matching default for platform])],
+               [AC_MSG_ERROR([invalid default])])
+            $4=m4_default([$7],NO)])],
+        [$4="$$4Default"])])
 
 # FP_LEADING_UNDERSCORE
 # ---------------------
@@ -1293,30 +1335,19 @@ AC_SUBST(GccLT46)
 
 dnl Check to see if the C compiler is clang or llvm-gcc
 dnl
-GccIsClang=NO
 AC_DEFUN([FP_CC_LLVM_BACKEND],
 [AC_REQUIRE([AC_PROG_CC])
-AC_MSG_CHECKING([whether C compiler is clang])
+AC_MSG_CHECKING([whether C compiler has an LLVM back end])
 $CC -x c /dev/null -dM -E > conftest.txt 2>&1
-if grep "__clang__" conftest.txt >/dev/null 2>&1; then
-  AC_SUBST([CC_CLANG_BACKEND], [1])
-  AC_SUBST([CC_LLVM_BACKEND], [1])
-  GccIsClang=YES
+if grep "__llvm__" conftest.txt >/dev/null 2>&1; then
+  AC_DEFINE([CC_LLVM_BACKEND], [1], [Define (to 1) if C compiler has an LLVM back end])
+  CcLlvmBackend=YES
   AC_MSG_RESULT([yes])
 else
+  CcLlvmBackend=NO
   AC_MSG_RESULT([no])
-  AC_MSG_CHECKING([whether C compiler has an LLVM back end])
-  if grep "__llvm__" conftest.txt >/dev/null 2>&1; then
-    AC_SUBST([CC_CLANG_BACKEND], [0])
-    AC_SUBST([CC_LLVM_BACKEND], [1])
-    AC_MSG_RESULT([yes])
-  else
-    AC_SUBST([CC_CLANG_BACKEND], [0])
-    AC_SUBST([CC_LLVM_BACKEND], [0])
-    AC_MSG_RESULT([no])
-  fi
 fi
-AC_SUBST(GccIsClang)
+AC_SUBST(CcLlvmBackend)
 
 rm -f conftest.txt
 ])
diff --git a/configure.ac b/configure.ac
index 6f1f0543d7..6fddd04bb0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -241,25 +241,27 @@ AC_SUBST(SOLARIS_BROKEN_SHLD)
 
 dnl ** Do an unregisterised build?
 dnl --------------------------------------------------------------
+
+AC_MSG_CHECKING(whether target supports a registerised ABI)
 case "$TargetArch" in
     i386|x86_64|powerpc|powerpc64|powerpc64le|arm|aarch64)
         UnregisterisedDefault=NO
+        AC_MSG_RESULT([yes])
         ;;
     *)
         UnregisterisedDefault=YES
+        AC_MSG_RESULT([no])
         ;;
 esac
-AC_ARG_ENABLE(unregisterised,
-[AC_HELP_STRING([--enable-unregisterised],
-[Build an unregisterised compiler (enabled by default on platforms without registerised support) [default="$UnregisterisedDefault"]])],
-[ if test x"$enableval" = x"yes"; then
-        Unregisterised=YES
-  else
-        Unregisterised=NO
-  fi
-],
-[Unregisterised="$UnregisterisedDefault"]
-)
+FP_DEFAULT_CHOICE_OVERRIDE_CHECK(
+  [unregisterised],
+  [unregisterised],
+  [registerised],
+  [Unregisterised],
+  [Build a toolchain with the unregisterised ABI (disabled by default on platforms with registerised support)],
+  [NO],
+  [YES],
+  [no])
 AC_SUBST(Unregisterised)
 
 dnl ** Do a build with tables next to code?
@@ -272,43 +274,35 @@ dnl decided by options to the compiler later.
 dnl
 dnl See https://gitlab.haskell.org/ghc/ghc/wikis/commentary/rts/storage/heap-objects#tables_next_to_code
 dnl --------------------------------------------------------------
+
+AC_MSG_CHECKING(whether target supports tables next to code)
 case "$Unregisterised" in
     NO)
         case "$TargetArch" in
             ia64|powerpc64|powerpc64le)
                 TablesNextToCodeDefault=NO
+                AC_MSG_RESULT([no])
                 ;;
             *)
                 TablesNextToCodeDefault=YES
+                AC_MSG_RESULT([yes])
                 ;;
         esac
         ;;
     YES)
         TablesNextToCodeDefault=NO
+        AC_MSG_RESULT([no])
         ;;
 esac
-AC_ARG_ENABLE(tables-next-to-code,
-[AC_HELP_STRING([--enable-tables-next-to-code],
-[Build an tables-next-to-code compiler (enabled by default on platforms without registerised support) [default="$TablesNextToCodeDefault"]])],
-[ if test x"$enableval" = x"yes"; then
-        TablesNextToCode=YES
-  else
-        TablesNextToCode=NO
-  fi
-],
-[TablesNextToCode="$TablesNextToCodeDefault"]
-)
-
-fail() {
-    echo >&2
-    echo "$1" >&2
-    exit 1
-}
-
-if test "$TablesNextToCodeDefault" = "NO" && test "$TablesNextToCode" = "YES"; then
-    fail "Error: tables next to code was requested but is not supported"
+FP_DEFAULT_CHOICE_OVERRIDE_CHECK(
+  [tables-next-to-code],
+  [tables next to code],
+  [tables apart from code],
+  [TablesNextToCode],
+  [Build a tool chain with info tables layed out next to code (enabled by default when using the registerised ABI, on platforms that support it)])
+if test x"$TablesNextToCode" = xYES; then
+   AC_DEFINE([TABLES_NEXT_TO_CODE], [1], [Define to 1 if info tables are layed out next to code])
 fi
-
 AC_SUBST(TablesNextToCode)
 
 dnl ** Does target have runtime linker support?
@@ -389,7 +383,7 @@ set_up_tarballs() {
         find "${base_dir}" -name "*.tar.xz" -exec tar xfJ {} \; &&
         rm ".MTREE" &&
         rm ".PKGINFO" &&
-        cd .. ) || fail "Error: Could not extract Windows toolchains."
+        cd .. ) || AC_MSG_ERROR([Could not extract Windows toolchains.])
 
         mv "inplace/${tarball_mingw_dir}" inplace/mingw &&
         touch inplace/mingw
@@ -1373,11 +1367,7 @@ echo "\
 "
 
 if test "x$CC_LLVM_BACKEND" = "x1"; then
-    if test "x$CC_CLANG_BACKEND" = "x1"; then
-        CompilerName="clang        "
-    else
-        CompilerName="llvm-gcc     "
-    fi
+    CompilerName="clang        "
 else
     CompilerName="gcc          "
 fi
diff --git a/hadrian/cfg/system.config.in b/hadrian/cfg/system.config.in
index 5d6d28d5f4..80fc3a3043 100644
--- a/hadrian/cfg/system.config.in
+++ b/hadrian/cfg/system.config.in
@@ -34,9 +34,7 @@ python         = python3
 #============================
 
 ar-supports-at-file = @ArSupportsAtFile@
-cc-clang-backend    = @CC_CLANG_BACKEND@
-cc-llvm-backend     = @CC_LLVM_BACKEND@
-gcc-is-clang        = @GccIsClang@
+cc-llvm-backend     = @CcLlvmBackend@
 hs-cpp-args         = @HaskellCPPArgs@
 
 # Build options:
diff --git a/hadrian/src/Oracles/Flag.hs b/hadrian/src/Oracles/Flag.hs
index 075a1bfe23..93babda794 100644
--- a/hadrian/src/Oracles/Flag.hs
+++ b/hadrian/src/Oracles/Flag.hs
@@ -11,7 +11,7 @@ import Oracles.Setting
 
 data Flag = ArSupportsAtFile
           | CrossCompiling
-          | GccIsClang
+          | CcLlvmBackend
           | GhcUnregisterised
           | TablesNextToCode
           | GmpInTree
@@ -23,13 +23,13 @@ data Flag = ArSupportsAtFile
           | UseSystemFfi
 
 -- Note, if a flag is set to empty string we treat it as set to NO. This seems
--- fragile, but some flags do behave like this, e.g. GccIsClang.
+-- fragile, but some flags do behave like this.
 flag :: Flag -> Action Bool
 flag f = do
     let key = case f of
             ArSupportsAtFile   -> "ar-supports-at-file"
             CrossCompiling     -> "cross-compiling"
-            GccIsClang         -> "gcc-is-clang"
+            CcLlvmBackend      -> "cc-llvm-backend"
             GhcUnregisterised  -> "ghc-unregisterised"
             TablesNextToCode   -> "tables-next-to-code"
             GmpInTree          -> "intree-gmp"
diff --git a/hadrian/src/Oracles/Setting.hs b/hadrian/src/Oracles/Setting.hs
index 2a4f5d0572..c84400ac69 100644
--- a/hadrian/src/Oracles/Setting.hs
+++ b/hadrian/src/Oracles/Setting.hs
@@ -25,8 +25,6 @@ data Setting = BuildArch
              | BuildOs
              | BuildPlatform
              | BuildVendor
-             | CcClangBackend
-             | CcLlvmBackend
              | CursesLibDir
              | DynamicExtension
              | FfiIncludeDir
@@ -113,8 +111,6 @@ setting key = lookupValueOrError configFile $ case key of
     BuildOs            -> "build-os"
     BuildPlatform      -> "build-platform"
     BuildVendor        -> "build-vendor"
-    CcClangBackend     -> "cc-clang-backend"
-    CcLlvmBackend      -> "cc-llvm-backend"
     CursesLibDir       -> "curses-lib-dir"
     DynamicExtension   -> "dynamic-extension"
     FfiIncludeDir      -> "ffi-include-dir"
diff --git a/hadrian/src/Rules/Generate.hs b/hadrian/src/Rules/Generate.hs
index 3faafbaaf7..e185a46ea5 100644
--- a/hadrian/src/Rules/Generate.hs
+++ b/hadrian/src/Rules/Generate.hs
@@ -379,20 +379,10 @@ generateGhcAutoconfH :: Expr String
 generateGhcAutoconfH = do
     trackGenerateHs
     configHContents  <- expr $ map undefinePackage <$> readFileLines configH
-    tablesNextToCode <- getFlag    TablesNextToCode
-    ghcUnreg         <- getFlag    GhcUnregisterised
-    ccLlvmBackend    <- getSetting CcLlvmBackend
-    ccClangBackend   <- getSetting CcClangBackend
     return . unlines $
         [ "#if !defined(__GHCAUTOCONF_H__)"
         , "#define __GHCAUTOCONF_H__" ]
         ++ configHContents ++
-        [ "\n#define TABLES_NEXT_TO_CODE 1" | tablesNextToCode && not ghcUnreg ]
-        ++
-        [ "\n#define llvm_CC_FLAVOR 1"      | ccLlvmBackend == "1" ]
-        ++
-        [ "\n#define clang_CC_FLAVOR 1"     | ccClangBackend == "1" ]
-        ++
         [ "#endif /* __GHCAUTOCONF_H__ */" ]
   where
     undefinePackage s
diff --git a/hadrian/src/Settings/Builders/Common.hs b/hadrian/src/Settings/Builders/Common.hs
index 7d9e0fe716..2c41d92493 100644
--- a/hadrian/src/Settings/Builders/Common.hs
+++ b/hadrian/src/Settings/Builders/Common.hs
@@ -53,9 +53,9 @@ cArgs = mempty
 cWarnings :: Args
 cWarnings = mconcat
     [ arg "-Wall"
-    , flag GccIsClang ? arg "-Wno-unknown-pragmas"
-    , notM (flag GccIsClang) ? not windowsHost ? arg "-Werror=unused-but-set-variable"
-    , notM (flag GccIsClang) ? arg "-Wno-error=inline" ]
+    , flag CcLlvmBackend ? arg "-Wno-unknown-pragmas"
+    , notM (flag CcLlvmBackend) ? not windowsHost ? arg "-Werror=unused-but-set-variable"
+    , notM (flag CcLlvmBackend) ? arg "-Wno-error=inline" ]
 
 packageDatabaseArgs :: Args
 packageDatabaseArgs = do
diff --git a/hadrian/src/Settings/Packages.hs b/hadrian/src/Settings/Packages.hs
index 94a586444d..ac3c28404e 100644
--- a/hadrian/src/Settings/Packages.hs
+++ b/hadrian/src/Settings/Packages.hs
@@ -106,7 +106,7 @@ packageArgs = do
         , package ghcPrim ? mconcat
           [ builder (Cabal Flags) ? arg "include-ghc-prim"
 
-          , builder (Cc CompileC) ? (not <$> flag GccIsClang) ?
+          , builder (Cc CompileC) ? (not <$> flag CcLlvmBackend) ?
             input "**/cbits/atomic.c"  ? arg "-Wno-sync-nand" ]
 
         --------------------------------- ghci ---------------------------------
@@ -278,10 +278,10 @@ rtsPackageArgs = package rts ? do
             -- any warnings in the module. See:
             -- https://gitlab.haskell.org/ghc/ghc/wikis/working-conventions#Warnings
 
-            , (not <$> flag GccIsClang) ?
+            , (not <$> flag CcLlvmBackend) ?
               inputs ["**/Compact.c"] ? arg "-finline-limit=2500"
 
-            , input "**/RetainerProfile.c" ? flag GccIsClang ?
+            , input "**/RetainerProfile.c" ? flag CcLlvmBackend ?
               arg "-Wno-incompatible-pointer-types"
             , windowsHost ? arg ("-DWINVER=" ++ windowsVersion)
 
diff --git a/hadrian/src/Settings/Warnings.hs b/hadrian/src/Settings/Warnings.hs
index ea89fea3ef..0d654411c4 100644
--- a/hadrian/src/Settings/Warnings.hs
+++ b/hadrian/src/Settings/Warnings.hs
@@ -11,10 +11,10 @@ import Settings
 defaultGhcWarningsArgs :: Args
 defaultGhcWarningsArgs = mconcat
     [ notStage0 ? arg "-Wnoncanonical-monad-instances"
-    , (not <$> flag GccIsClang) ? mconcat
+    , (not <$> flag CcLlvmBackend) ? mconcat
       [ not windowsHost ? arg "-optc-Werror=unused-but-set-variable"
       , arg "-optc-Wno-error=inline" ]
-    , flag GccIsClang ? arg "-optc-Wno-unknown-pragmas" ]
+    , flag CcLlvmBackend ? arg "-optc-Wno-unknown-pragmas" ]
 
 -- | Package-specific warnings-related arguments, mostly suppressing various warnings.
 ghcWarningsArgs :: Args
diff --git a/includes/Stg.h b/includes/Stg.h
index 7f1764a944..73de97055f 100644
--- a/includes/Stg.h
+++ b/includes/Stg.h
@@ -61,7 +61,7 @@
 # define _DEFAULT_SOURCE
 #endif
 
-#if IN_STG_CODE == 0 || defined(llvm_CC_FLAVOR)
+#if IN_STG_CODE == 0 || defined(CC_LLVM_BACKEND)
 // C compilers that use an LLVM back end (clang or llvm-gcc) do not
 // correctly support global register variables so we make sure that
 // we do not declare them for these compilers.
diff --git a/includes/ghc.mk b/includes/ghc.mk
index eee72128b0..f8da99abb6 100644
--- a/includes/ghc.mk
+++ b/includes/ghc.mk
@@ -114,23 +114,6 @@ $$(includes_$1_H_CONFIG) : mk/config.h mk/config.mk includes/ghc.mk | $$$$(dir $
 #
 	@sed 's,^\([	 ]*\)#[	 ]*define[	 ][	 ]*\(PACKAGE_[A-Z]*\)[	 ][ 	]*".*".*$$$$,\1/* #undef \2 */,' mk/config.h >> $$@
 #
-#	Tack on some extra config information from the build system
-#
-ifeq "$$(TablesNextToCode)" "YES"
-	@echo >> $$@
-	@echo "#define TABLES_NEXT_TO_CODE 1" >> $$@
-endif
-#
-ifeq "$$(CC_LLVM_BACKEND)" "1"
-	@echo >> $$@
-	@echo "#define llvm_CC_FLAVOR 1" >> $$@
-endif
-#
-ifeq "$$(CC_CLANG_BACKEND)" "1"
-	@echo >> $$@
-	@echo "#define clang_CC_FLAVOR 1" >> $$@
-endif
-#
 	@echo "#endif /* __GHCAUTOCONF_H__ */"          >> $$@
 	@echo "Done."
 
diff --git a/mk/config.mk.in b/mk/config.mk.in
index a946b17bf9..8bbfde2e26 100644
--- a/mk/config.mk.in
+++ b/mk/config.mk.in
@@ -527,7 +527,9 @@ GccVersion            = @GccVersion@
 # the necessary format to pass to libffi's configure.
 TargetPlatformFull    = @TargetPlatformFull@
 GccLT46         = @GccLT46@
-GccIsClang      = @GccIsClang@
+
+# Do we have a C compiler using an LLVM back end?
+CcLlvmBackend   = @CcLlvmBackend@
 
 CC              = @CC@
 CC_STAGE0       = @CC_STAGE0@
diff --git a/mk/project.mk.in b/mk/project.mk.in
index 5cc2e4aeb1..9ee2eab59f 100644
--- a/mk/project.mk.in
+++ b/mk/project.mk.in
@@ -153,10 +153,6 @@ endif
 # linker or not?
 SOLARIS_BROKEN_SHLD=@SOLARIS_BROKEN_SHLD@
 
-# Do we have a C compiler using an LLVM back end?
-CC_LLVM_BACKEND  = @CC_LLVM_BACKEND@
-CC_CLANG_BACKEND = @CC_CLANG_BACKEND@
-
 # Is the stage0 compiler affected by Bug #9439?
 GHC_LLVM_AFFECTED_BY_9439 = @GHC_LLVM_AFFECTED_BY_9439@
 
diff --git a/mk/warnings.mk b/mk/warnings.mk
index 323ea75898..cee408d061 100644
--- a/mk/warnings.mk
+++ b/mk/warnings.mk
@@ -17,7 +17,7 @@ GhcRtsHcOpts    += -Wcpp-undef
 GhcStage1HcOpts += -Wcpp-undef
 GhcStage2HcOpts += -Wcpp-undef
 
-ifneq "$(GccIsClang)" "YES"
+ifneq "$(CcLlvmBackend)" "YES"
 
 # Debian doesn't turn -Werror=unused-but-set-variable on by default, so
 # we turn it on explicitly for consistency with other users
diff --git a/rts/Task.h b/rts/Task.h
index 88b567ab87..17bcbe2da4 100644
--- a/rts/Task.h
+++ b/rts/Task.h
@@ -271,7 +271,7 @@ extern uint32_t peakWorkerCount;
 #if ((defined(linux_HOST_OS) && \
      (defined(i386_HOST_ARCH) || defined(x86_64_HOST_ARCH))) || \
     (defined(mingw32_HOST_OS) && __GNUC__ >= 4 && __GNUC_MINOR__ >= 4)) && \
-    (!defined(llvm_CC_FLAVOR))
+    (!defined(CC_LLVM_BACKEND))
 #define MYTASK_USE_TLV
 extern __thread Task *my_task;
 #else
diff --git a/rts/ghc.mk b/rts/ghc.mk
index 26865b5bb7..c07cfaec86 100644
--- a/rts/ghc.mk
+++ b/rts/ghc.mk
@@ -523,7 +523,7 @@ rts/win32/ThrIOManager_CC_OPTS += -w
 # for details
 
 # Without this, thread_obj will not be inlined (at least on x86 with GCC 4.1.0)
-ifneq "$(CC_CLANG_BACKEND)" "1"
+ifneq "$(CcLlvmBackend)" "YES"
 rts/sm/Compact_CC_OPTS += -finline-limit=2500
 endif
 
diff --git a/rts/sm/GCTDecl.h b/rts/sm/GCTDecl.h
index 8306795ade..e740392c15 100644
--- a/rts/sm/GCTDecl.h
+++ b/rts/sm/GCTDecl.h
@@ -52,11 +52,11 @@ extern StgWord8 the_gc_thread[];
 
 /* Now, llvm-gcc and some older Clang compilers do not support
    __thread. So we have to fallback to the extremely slow case,
-   unfortunately. Note: clang_CC_FLAVOR implies llvm_CC_FLAVOR.
+   unfortunately.
 
    Also, the iOS Clang compiler doesn't support __thread either for
    some bizarre reason, so there's not much we can do about that... */
-#if defined(llvm_CC_FLAVOR) && (CC_SUPPORTS_TLS == 0)
+#if defined(CC_LLVM_BACKEND) && (CC_SUPPORTS_TLS == 0)
 #define gct ((gc_thread *)(pthread_getspecific(gctKey)))
 #define SET_GCT(to) (pthread_setspecific(gctKey, to))
 #define DECLARE_GCT ThreadLocalKey gctKey;
@@ -66,7 +66,7 @@ extern StgWord8 the_gc_thread[];
 /* However, if we *are* using an LLVM based compiler with __thread
    support, then use that (since LLVM doesn't support global register
    variables.) */
-#elif defined(llvm_CC_FLAVOR) && (CC_SUPPORTS_TLS == 1)
+#elif defined(CC_LLVM_BACKEND) && (CC_SUPPORTS_TLS == 1)
 extern __thread gc_thread* gct;
 #define SET_GCT(to) gct = (to)
 #define DECLARE_GCT __thread gc_thread* gct;
diff --git a/rts/sm/GCThread.h b/rts/sm/GCThread.h
index 66f604d6cc..66f7a7f84f 100644
--- a/rts/sm/GCThread.h
+++ b/rts/sm/GCThread.h
@@ -208,7 +208,7 @@ extern uint32_t n_gc_threads;
 
 extern gc_thread **gc_threads;
 
-#if defined(THREADED_RTS) && defined(llvm_CC_FLAVOR)
+#if defined(THREADED_RTS) && defined(CC_LLVM_BACKEND)
 extern ThreadLocalKey gctKey;
 #endif
 
diff --git a/rts/sm/Storage.c b/rts/sm/Storage.c
index d4be531c73..0130a08f7c 100644
--- a/rts/sm/Storage.c
+++ b/rts/sm/Storage.c
@@ -271,7 +271,7 @@ void storageAddCapabilities (uint32_t from, uint32_t to)
         }
     }
 
-#if defined(THREADED_RTS) && defined(llvm_CC_FLAVOR) && (CC_SUPPORTS_TLS == 0)
+#if defined(THREADED_RTS) && defined(CC_LLVM_BACKEND) && (CC_SUPPORTS_TLS == 0)
     newThreadLocalKey(&gctKey);
 #endif
 
@@ -295,7 +295,7 @@ freeStorage (bool free_heap)
     closeMutex(&sm_mutex);
 #endif
     stgFree(nurseries);
-#if defined(THREADED_RTS) && defined(llvm_CC_FLAVOR) && (CC_SUPPORTS_TLS == 0)
+#if defined(THREADED_RTS) && defined(CC_LLVM_BACKEND) && (CC_SUPPORTS_TLS == 0)
     freeThreadLocalKey(&gctKey);
 #endif
     freeGcThreads();