diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -465,17 +465,17 @@
 add_target_flags_if(LIBCXX_BUILD_32_BITS "-m32")
 
 if(LIBCXX_TARGET_TRIPLE)
-  add_target_flags("--target=${LIBCXX_TARGET_TRIPLE}")
+  add_target_flags_if_supported("--target=${LIBCXX_TARGET_TRIPLE}")
 elseif(CMAKE_CXX_COMPILER_TARGET)
   set(LIBCXX_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBCXX_SYSROOT)
-  add_target_flags("--sysroot=${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("--gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")
+  add_target_flags_if_supported("--gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")
 elseif(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
   set(LIBCXX_GCC_TOOLCHAIN "${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
 endif()
diff --git a/libcxx/cmake/Modules/HandleLibcxxFlags.cmake b/libcxx/cmake/Modules/HandleLibcxxFlags.cmake
--- a/libcxx/cmake/Modules/HandleLibcxxFlags.cmake
+++ b/libcxx/cmake/Modules/HandleLibcxxFlags.cmake
@@ -121,6 +121,17 @@
   endif()
 endmacro()
 
+# Add all the flags supported by the compiler to all of
+# 'CMAKE_CXX_FLAGS', 'CMAKE_C_FLAGS', 'LIBCXX_COMPILE_FLAGS'
+# and 'LIBCXX_LINK_FLAGS'.
+macro(add_target_flags_if_supported)
+  foreach(flag ${ARGN})
+    mangle_name("${flag}" flagname)
+    check_cxx_compiler_flag("${flag}" "LIBCXX_SUPPORTS_${flagname}_FLAG")
+    add_target_flags_if(LIBCXX_SUPPORTS_${flagname}_FLAG ${flag})
+  endforeach()
+endmacro()
+
 # Add a specified list of flags to both 'LIBCXX_COMPILE_FLAGS' and
 # 'LIBCXX_LINK_FLAGS'.
 macro(add_flags)
diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -258,17 +258,17 @@
 add_target_flags_if(LIBCXXABI_BUILD_32_BITS "-m32")
 
 if(LIBCXXABI_TARGET_TRIPLE)
-  add_target_flags("--target=${LIBCXXABI_TARGET_TRIPLE}")
+  add_target_flags_if_supported("--target=${LIBCXXABI_TARGET_TRIPLE}")
 elseif(CMAKE_CXX_COMPILER_TARGET)
   set(LIBCXXABI_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBCXX_GCC_TOOLCHAIN)
-  add_target_flags("--gcc-toolchain=${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("--sysroot=${LIBCXXABI_SYSROOT}")
+  add_target_flags_if_supported("--sysroot=${LIBCXXABI_SYSROOT}")
 elseif(CMAKE_SYSROOT)
   set(LIBCXXABI_SYSROOT "${CMAKE_SYSROOT}")
 endif()
diff --git a/libcxxabi/cmake/Modules/HandleLibcxxabiFlags.cmake b/libcxxabi/cmake/Modules/HandleLibcxxabiFlags.cmake
--- a/libcxxabi/cmake/Modules/HandleLibcxxabiFlags.cmake
+++ b/libcxxabi/cmake/Modules/HandleLibcxxabiFlags.cmake
@@ -123,6 +123,17 @@
   endif()
 endmacro()
 
+# Add all the flags supported by the compiler to all of
+# 'CMAKE_CXX_FLAGS', 'CMAKE_C_FLAGS', 'LIBCXXABI_COMPILE_FLAGS'
+# and 'LIBCXXABI_LINK_FLAGS'.
+macro(add_target_flags_if_supported)
+  foreach(flag ${ARGN})
+    mangle_name("${flag}" flagname)
+    check_cxx_compiler_flag("${flag}" "LIBCXXABI_SUPPORTS_${flagname}_FLAG")
+    add_target_flags_if(LIBCXXABI_SUPPORTS_${flagname}_FLAG ${flag})
+  endforeach()
+endmacro()
+
 # Add a specified list of flags to both 'LIBCXXABI_COMPILE_FLAGS' and
 # 'LIBCXXABI_LINK_FLAGS'.
 macro(add_flags)
diff --git a/libunwind/CMakeLists.txt b/libunwind/CMakeLists.txt
--- a/libunwind/CMakeLists.txt
+++ b/libunwind/CMakeLists.txt
@@ -152,17 +152,17 @@
 add_target_flags_if(LIBUNWIND_BUILD_32_BITS "-m32")
 
 if(LIBUNWIND_TARGET_TRIPLE)
-  add_target_flags("--target=${LIBUNWIND_TARGET_TRIPLE}")
+  add_target_flags_if_supported("--target=${LIBUNWIND_TARGET_TRIPLE}")
 elseif(CMAKE_CXX_COMPILER_TARGET)
   set(LIBUNWIND_TARGET_TRIPLE "${CMAKE_CXX_COMPILER_TARGET}")
 endif()
 if(LIBUNWIND_GCC_TOOLCHAIN)
-  add_target_flags("--gcc-toolchain=${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("--sysroot=${LIBUNWIND_SYSROOT}")
+  add_target_flags_if_supported("--sysroot=${LIBUNWIND_SYSROOT}")
 elseif(CMAKE_SYSROOT)
   set(LIBUNWIND_SYSROOT "${CMAKE_SYSROOT}")
 endif()
diff --git a/libunwind/cmake/Modules/HandleLibunwindFlags.cmake b/libunwind/cmake/Modules/HandleLibunwindFlags.cmake
--- a/libunwind/cmake/Modules/HandleLibunwindFlags.cmake
+++ b/libunwind/cmake/Modules/HandleLibunwindFlags.cmake
@@ -124,6 +124,17 @@
   endif()
 endmacro()
 
+# Add all the flags supported by the compiler to all of
+# 'CMAKE_CXX_FLAGS', 'CMAKE_C_FLAGS', 'LIBUNWIND_COMPILE_FLAGS'
+# and 'LIBUNWIND_LINK_FLAGS'.
+macro(add_target_flags_if_supported)
+  foreach(flag ${ARGN})
+    mangle_name("${flag}" flagname)
+    check_cxx_compiler_flag("${flag}" "LIBUNWIND_SUPPORTS_${flagname}_FLAG")
+    add_target_flags_if(LIBUNWIND_SUPPORTS_${flagname}_FLAG ${flag})
+  endforeach()
+endmacro()
+
 # Add a specified list of flags to both 'LIBUNWIND_COMPILE_FLAGS' and
 # 'LIBUNWIND_LINK_FLAGS'.
 macro(add_flags)