With unquoted ${CMAKE_CXX_FLAGS}, the REGEX fails when it's empty:
```CMake Error at lib/scudo/standalone/CMakeLists.txt:14 (string):
string sub-command REGEX, mode REPLACE needs at least 6 arguments total to
command.```
# append_list_if(COMPILER_RT_HAS_SANITIZER_COMMON ${SANITIZER_COMMON_CFLAGS} GWP_ASAN_CFLAGS)
# Remove -stdlib= which is unused when passing -nostdinc++.
-string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
# Options parsing support is optional. This is an optional library that can be
# used by an allocator to automatically parse GwpAsan options from the
# We don't use the C++ Standard Library here, so avoid including it by mistake.
append_list_if(COMPILER_RT_HAS_NOSTDINCXX_FLAG -nostdinc++ EXTRA_FLAGS)
# XRay uses C++ standard library headers.
-string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
# This appears to be a C-only warning banning the use of locals in aggregate
# initializers. All other compilers accept this, though.
-nostdinc++)
# Remove -stdlib= which is unused when passing -nostdinc++.
-string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
append_list_if(COMPILER_RT_HAS_FVISIBILITY_HIDDEN_FLAG -fvisibility=hidden SCUDO_CFLAGS)