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

[Ian Anderson via cfe-commits]

================
@@ -1,3 +1,4 @@
+// REQUIRES: default-cxx-stdlib=libstdc++
----------------
ian-twilightcoder wrote:

Maybe this should be `!=libc++` instead?

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