[clang] [C++17] Support __GCC_[CON|DE]STRUCTIVE_SIZE (PR #89446)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

Precommit CI is currently failing on libc++ tests that are impacted by this change; should I solve those as part of this patch or are you okay with fixing those after this patch lands? (Or would you like to push a fix to this branch?)

https://github.com/llvm/llvm-project/pull/89446