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

[Corentin Jabot via cfe-commits]

cor3ntin wrote:

@AaronBallman there is a PR that needs something similar for msvc https://github.com/llvm/llvm-project/pull/194201/changes - and as i said earlier there are a few other places where we do things conditionally on macros being defined

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