[clang] [Clang] Support libstdc++ workarounds when using `-E` (PR #210802)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

This seems completely reasonable to me.  Get 1 more +1 from the others, else LGTM.

https://github.com/llvm/llvm-project/pull/210802