[libcxx] Allow target flags to affect CMake configuration tests

Summary:
This patch changes the libc++ CMake so that it adds certain target flags like '-m32' or '--gcc-toolchain' before including config-ix.cmake.
Since these flags can affect things like check_library_exists([...]) they needed to be added before the tests are performed.

This patch fixes:

https://llvm.org/bugs/show_bug.cgi?id=24322

Reviewers: danalbert, jroelofs, bcraig, compnerd

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D20887

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@271460 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -247,6 +247,18 @@ set(LIBCXX_COMPILE_FLAGS "")
 set(LIBCXX_LINK_FLAGS "")
 set(LIBCXX_LIBRARIES "")
 
+# Include macros for adding and removing libc++ flags.
+include(HandleLibcxxFlags)
+
+# Target flags ================================================================
+# These flags get added to CMAKE_CXX_FLAGS and CMAKE_C_FLAGS so that
+# '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")
+add_target_flags_if(LIBCXX_TARGET_TRIPLE "-target ${LIBCXX_TARGET_TRIPLE}")
+add_target_flags_if(LIBCXX_SYSROOT "--sysroot=${LIBCXX_SYSROOT}")
+add_target_flags_if(LIBCXX_GCC_TOOLCHAIN "-gcc-toolchain ${LIBCXX_GCC_TOOLCHAIN}")
+
 # Configure compiler.
 include(config-ix)
 
@@ -264,9 +276,6 @@ string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
 
 include(HandleLibCXXABI) # Setup the ABI library flags
 
-# Include macros for adding and removing libc++ flags.
-include(HandleLibcxxFlags)
-
 # Remove flags that may have snuck in.
 remove_flags(-DNDEBUG -UNDEBUG -D_DEBUG
              -stdlib=libc++ -stdlib=libstdc++ -lc++abi -m32)
@@ -288,11 +297,6 @@ endif()
 # headers
 add_compile_flags_if_supported(-nostdinc++)
 
-# Target flags ================================================================
-add_flags_if(LIBCXX_BUILD_32_BITS -m32)
-add_flags_if(LIBCXX_TARGET_TRIPLE "-target ${LIBCXX_TARGET_TRIPLE}")
-add_flags_if(LIBCXX_SYSROOT "--sysroot ${LIBCXX_SYSROOT}")
-add_flags_if(LIBCXX_GCC_TOOLCHAIN "-gcc-toolchain ${LIBCXX_GCC_TOOLCHAIN}")
 
 # Warning flags ===============================================================
 add_definitions(-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)

cmake/Modules/HandleLibcxxFlags.cmake

@@ -76,6 +76,26 @@ macro(config_define value def)
   set(LIBCXX_NEEDS_SITE_CONFIG ON)
 endmacro()
 
+# Add a list of flags to all of 'CMAKE_CXX_FLAGS', 'CMAKE_C_FLAGS',
+# 'LIBCXX_COMPILE_FLAGS' and 'LIBCXX_LINK_FLAGS'.
+macro(add_target_flags)
+  foreach(value ${ARGN})
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${value}")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${value}")
+    list(APPEND LIBCXX_COMPILE_FLAGS ${value})
+    list(APPEND LIBCXX_LINK_FLAGS ${value})
+  endforeach()
+endmacro()
+
+# If the specified 'condition' is true then add a list of flags to
+# all of 'CMAKE_CXX_FLAGS', 'CMAKE_C_FLAGS', 'LIBCXX_COMPILE_FLAGS'
+# and 'LIBCXX_LINK_FLAGS'.
+macro(add_target_flags_if condition)
+  if (${condition})
+    add_target_flags(${ARGN})
+  endif()
+endmacro()
+
 # Add a specified list of flags to both 'LIBCXX_COMPILE_FLAGS' and
 # 'LIBCXX_LINK_FLAGS'.
 macro(add_flags)