Drop Xcode 4.1 hack and fix ignored CC var issue

Xcode 4.1 was released back in 2011 for Mac OSX 10.6/10.7.
However, OSX 10.7 reached EOL sometime around the end of 2014.
So this `--with-gcc-4.2` hack shouldn't be needed anymore.

Moreover, this patch changes ./configure to honor the CC env-var
again (and thus fix #11231) while giving `--with-gcc=...` a higher
priority over `CC=...`.

So the following 3 invocations are equivalent now:

  CC=... ./configure
  ./configure CC=...
  ./configure --with-gcc=...

Since `--with-{gcc,clang}=...` is a misnomer (as is made apparent by
`--with-gcc=clang` or `--with-clang=gcc`), this would give us a neutral
and idiomatic way to tell ./configure which C compiler to use.

Moreover, `./configure --help` says at the end of its output:

  Some influential environment variables:
    CC		C compiler command
    CFLAGS	C compiler flags
    LDFLAGS	linker flags, e.g. -L<lib dir> if you have libraries in a
		nonstandard directory <lib dir>
    LIBS	libraries to pass to the linker, e.g. -l<library>
    CPPFLAGS	(Objective) C/C++ preprocessor flags, e.g. -I<include dir> if
		you have headers in a nonstandard directory <include dir>
    CPP		C preprocessor

  Use these variables to override the choices made by `configure' or to help
  it to find libraries and programs with nonstandard names/locations.

Consequently, by honoring CC=... (rather than ignoring it) we increase
consistency and reduce user confusion. Ideally, CC=... would become the
recommended way to set the C compiler, and `--with-{clang,gcc}=...`
would be demoted to legacy aliases.

Reviewed By: erikd, bgamari

Differential Revision: https://phabricator.haskell.org/D2046

1 files changed, 7 insertions, 10 deletions

diff --git a/aclocal.m4 b/aclocal.m4
index 14b848143f..5becadbbb4 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -2033,22 +2033,19 @@ AC_DEFUN([FIND_GHC_BOOTSTRAP_PROG],[
 # $2 = the with option name
 # $3 = the command to look for
 AC_DEFUN([FIND_GCC],[
-    if test "$TargetOS_CPP" = "darwin" &&
-       test "$XCodeVersion1" -eq 4 &&
-       test "$XCodeVersion2" -lt 2
-    then
-        # In Xcode 4.1, 'gcc-4.2' is the gcc legacy backend (rather
-        # than the LLVM backend). We prefer the legacy gcc, but in
-        # Xcode 4.2 'gcc-4.2' was removed.
-        FP_ARG_WITH_PATH_GNU_PROG([$1], [gcc-4.2], [gcc-4.2])
-    elif test "$windows" = YES
+    if test "$windows" = YES
     then
         $1="$CC"
     else
         FP_ARG_WITH_PATH_GNU_PROG_OPTIONAL([$1], [$2], [$3])
+        # fallback to CC if set and no --with-$2=... was used
+        if test -z "$With_$2" -a -n "$CC"
+        then
+            With_$2="$CC"
+            $1="$CC"
         # From Xcode 5 on/, OS X command line tools do not include gcc
         # anymore. Use clang.
-        if test -z "$$1"
+        elif test -z "$$1"
         then
             FP_ARG_WITH_PATH_GNU_PROG_OPTIONAL([$1], [clang], [clang])
         fi