cmake COMPILER_RT_HAS_EXTERNAL_FLAG examples

Lewuathe/mlir-hello thirdparty/llvm-project/compiler-rt/cmake/config-ix.cmake :153

check_cxx_compiler_flag("/experimental:external /external:W0" COMPILER_RT_HAS_EXTERNAL_FLAG)

CTSRD-CHERI/cheribsd contrib/subrepo-cheri-compiler-rt/cmake/config-ix.cmake :130

check_cxx_compiler_flag("/experimental:external /external:W0" COMPILER_RT_HAS_EXTERNAL_FLAG)