[clang] [Clang] Warn on deprecated specializations used in system headers. (PR #70353)

[Louis Dionne via cfe-commits]

ldionne wrote:

I'm not familiar with your exact setup, but I think you should probably report those warnings to Google Test and turn off deprecation warnings in your build with `-Wno-deprecated` until you're able to update to a version of Google Test that has fixed this issue?

https://github.com/llvm/llvm-project/pull/70353