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

[Jon Roelofs via cfe-commits]

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

I think it's fine. I'm not sure `REQUIRES` has a `!=`

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