[runtimes] Properly handle the sysroot/triple/gcc-toolchain

In 395271a, I simplified how we handled the target triple for the
runtimes. However, in doing so, we stopped considering the default
in CMAKE_CXX_COMPILER_TARGET, so we'd use the LLVM_DEFAULT_TARGET_TRIPLE
(which is the host triple) even if CMAKE_CXX_COMPILER_TARGET was specified.
This commit fixes that problem and also refactors the code so that it's
easy to see what the default value is.

The fact that nobody seems to have been broken by this makes me think
that perhaps nobody is using CMAKE_CXX_COMPILER_TARGET to specify the
triple -- but it should still work.

Differential Revision: https://reviews.llvm.org/D111672

(cherry picked from commit 72117f2ffeb6a096a808c34ec7ebee122c2d2e21)

3 files changed, 28 insertions, 29 deletions

diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index fd7eea06a9a1..5ef0a7727dde 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -256,9 +256,15 @@ option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." OFF)
 
 # Target options --------------------------------------------------------------
 option(LIBCXX_BUILD_32_BITS "Build 32 bit libc++." ${LLVM_BUILD_32_BITS})
-set(LIBCXX_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Use alternate target triple.")
-set(LIBCXX_SYSROOT "" CACHE STRING "Use alternate sysroot.")
-set(LIBCXX_GCC_TOOLCHAIN "" CACHE STRING "Use alternate GCC toolchain.")
+
+if(CMAKE_CXX_COMPILER_TARGET)
+  set(LIBCXX_DEFAULT_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
+else()
+  set(LIBCXX_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+endif()
+set(LIBCXX_TARGET_TRIPLE "${LIBCXX_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Use alternate target triple.")
+set(LIBCXX_SYSROOT "${CMAKE_SYSROOT}" CACHE STRING "Use alternate sysroot.")
+set(LIBCXX_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}" CACHE STRING "Use alternate GCC toolchain.")
 
 # Feature options -------------------------------------------------------------
 option(LIBCXX_ENABLE_EXCEPTIONS "Use exceptions." ON)
@@ -468,21 +474,14 @@ include(HandleLibcxxFlags)
 # 'config-ix' use them during feature checks. It also adds them to both
 # 'LIBCXX_COMPILE_FLAGS' and 'LIBCXX_LINK_FLAGS'
 add_target_flags_if(LIBCXX_BUILD_32_BITS "-m32")
-
 if(LIBCXX_TARGET_TRIPLE)
   add_target_flags_if_supported("--target=${LIBCXX_TARGET_TRIPLE}")
-elseif(CMAKE_CXX_COMPILER_TARGET)
-  set(LIBCXX_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBCXX_SYSROOT)
   add_target_flags_if_supported("--sysroot=${LIBCXX_SYSROOT}")
-elseif(CMAKE_SYSROOT)
-  set(LIBCXX_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 if(LIBCXX_GCC_TOOLCHAIN)
   add_target_flags_if_supported("--gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")
-elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
-  set(LIBCXX_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()
 
 # Configure compiler.
diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
index c5cc73dc3680..f3060a5d1f93 100644
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -111,9 +111,16 @@ option(LIBCXXABI_INCLUDE_TESTS "Generate build targets for the libc++abi unit te
 set(LIBCXXABI_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXXABI_INSTALL_LIBRARY "Install the libc++abi library." ON)
-set(LIBCXXABI_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
-set(LIBCXXABI_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
-set(LIBCXXABI_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
+
+if(CMAKE_CXX_COMPILER_TARGET)
+  set(LIBCXXABI_DEFAULT_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
+else()
+  set(LIBCXXABI_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+endif()
+set(LIBCXXABI_TARGET_TRIPLE "${LIBCXXABI_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
+set(LIBCXXABI_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}" CACHE PATH "GCC toolchain for cross compiling.")
+set(LIBCXXABI_SYSROOT "${CMAKE_SYSROOT}" CACHE PATH "Sysroot for cross compiling.")
+
 set(LIBCXXABI_LIBCXX_LIBRARY_PATH "" CACHE PATH "The path to libc++ library.")
 set(LIBCXXABI_LIBRARY_VERSION "1.0" CACHE STRING
 "Version of libc++abi. This will be reflected in the name of the shared \
@@ -259,18 +266,12 @@ add_target_flags_if(LIBCXXABI_BUILD_32_BITS "-m32")
 
 if(LIBCXXABI_TARGET_TRIPLE)
   add_target_flags_if_supported("--target=${LIBCXXABI_TARGET_TRIPLE}")
-elseif(CMAKE_CXX_COMPILER_TARGET)
-  set(LIBCXXABI_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
-if(LIBCXX_GCC_TOOLCHAIN)
+if(LIBCXXABI_GCC_TOOLCHAIN)
   add_target_flags_if_supported("--gcc-toolchain=${LIBCXXABI_GCC_TOOLCHAIN}")
-elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
-  set(LIBCXXABI_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()
 if(LIBCXXABI_SYSROOT)
   add_target_flags_if_supported("--sysroot=${LIBCXXABI_SYSROOT}")
-elseif(CMAKE_SYSROOT)
-  set(LIBCXXABI_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 
 # Configure compiler. Must happen after setting the target flags.
diff --git a/libunwind/CMakeLists.txt b/libunwind/CMakeLists.txt
index f32fe9d13fc1..aa47fd28aa82 100644
--- a/libunwind/CMakeLists.txt
+++ b/libunwind/CMakeLists.txt
@@ -77,9 +77,14 @@ cmake_dependent_option(LIBUNWIND_INSTALL_STATIC_LIBRARY
 cmake_dependent_option(LIBUNWIND_INSTALL_SHARED_LIBRARY
   "Install the shared libunwind library." ON
   "LIBUNWIND_ENABLE_SHARED;LIBUNWIND_INSTALL_LIBRARY" OFF)
-set(LIBUNWIND_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
-set(LIBUNWIND_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
-set(LIBUNWIND_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
+if(CMAKE_CXX_COMPILER_TARGET)
+  set(LIBUNWIND_DEFAULT_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
+else()
+  set(LIBUNWIND_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+endif()
+set(LIBUNWIND_TARGET_TRIPLE "${LIBUNWIND_DEFAULT_TARGET_TRIPLE}" CACHE STRING "Target triple for cross compiling.")
+set(LIBUNWIND_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}" CACHE PATH "GCC toolchain for cross compiling.")
+set(LIBUNWIND_SYSROOT "${CMAKE_SYSROOT}" CACHE PATH "Sysroot for cross compiling.")
 set(LIBUNWIND_TEST_LINKER_FLAGS "" CACHE STRING
     "Additional linker flags for test programs.")
 set(LIBUNWIND_TEST_COMPILER_FLAGS "" CACHE STRING
@@ -153,18 +158,12 @@ add_target_flags_if(LIBUNWIND_BUILD_32_BITS "-m32")
 
 if(LIBUNWIND_TARGET_TRIPLE)
   add_target_flags_if_supported("--target=${LIBUNWIND_TARGET_TRIPLE}")
-elseif(CMAKE_CXX_COMPILER_TARGET)
-  set(LIBUNWIND_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBUNWIND_GCC_TOOLCHAIN)
   add_target_flags_if_supported("--gcc-toolchain=${LIBUNWIND_GCC_TOOLCHAIN}")
-elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
-  set(LIBUNWIND_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()
 if(LIBUNWIND_SYSROOT)
   add_target_flags_if_supported("--sysroot=${LIBUNWIND_SYSROOT}")
-elseif(CMAKE_SYSROOT)
-  set(LIBUNWIND_SYSROOT "${CMAKE_SYSROOT}")
 endif()
 
 # Configure compiler.