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

[Corentin Jabot via cfe-commits]

cor3ntin wrote:

Right, Ambrose did not inject __GLIBCXX__ as a predefined macro, and as we generalize we should keep not adding these non-macros to the preprocessor state. they are _only_ observed by the bits of clang that have workaround / logic based on them being defined. Further erroring on any identifier we don't recognize makes sense to me

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