[CMake] Remove -stdlib= which is unused when passing -nostdinc++

[Hahnfeld]

Summary

This avoids the warnings when building with LLVM_ENABLE_LIBCXX
which automatically adds -stdlib=libc++ to CMAKE_CXX_FLAGS.

[Hahnfeld]

Rebase and fix typo.

[Hahnfeld]

ping

[beanz]

LGTM

lib/fuzzer/CMakeLists.txt

CHECK_CXX_SOURCE_COMPILES("
   return 0;
   }
   " HAS_THREAD_LOCAL)
 
 set(LIBFUZZER_CFLAGS ${SANITIZER_COMMON_CFLAGS})
 
 if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND COMPILER_RT_LIBCXX_PATH)
   list(APPEND LIBFUZZER_CFLAGS -nostdinc++ -D_LIBCPP_ABI_VERSION=Fuzzer)
+  # Remove -stdlib= which is unused when passing -nostdinc++.
+  string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
 endif()
 
 append_list_if(COMPILER_RT_HAS_OMIT_FRAME_POINTER_FLAG -fno-omit-frame-pointer LIBFUZZER_CFLAGS)
 
 if (CMAKE_CXX_FLAGS MATCHES "fsanitize-coverage")
   list(APPEND LIBFUZZER_CFLAGS -fno-sanitize-coverage=trace-pc-guard,edge,trace-cmp,indirect-calls,8bit-counters)
 endif()
 

lib/msan/tests/CMakeLists.txt

set(MSAN_UNITTEST_COMMON_CFLAGS
   -mno-omit-leaf-frame-pointer
   -Wno-deprecated-declarations
   -Wno-unused-variable
   -Wno-zero-length-array
   -Wno-uninitialized
   -Werror=sign-compare
   -Wno-gnu-zero-variadic-macro-arguments
 )
+# Remove -stdlib= which is unused when passing -nostdinc++.
+string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+
 set(MSAN_UNITTEST_INSTRUMENTED_CFLAGS
   ${MSAN_UNITTEST_COMMON_CFLAGS}
   -fsanitize=memory
   -fsanitize-memory-track-origins
   -mllvm -msan-keep-going=1
 )
 set(MSAN_UNITTEST_LINK_FLAGS
   -fsanitize=memory