[clang] [test][Driver][clang] Fix darwin-embedded-search-paths.c when CLANG_DEFAULT_CXX_STDLIB is libc++ (PR #122145)

[Ian Anderson via cfe-commits]

ian-twilightcoder wrote:

Does anyone know a cleaner way of testing this besides just duplicating the test?

https://github.com/llvm/llvm-project/pull/122145