[clang] [BitInt] Expose a _BitInt literal suffix in C++ (PR #86586)

[Erich Keane via cfe-commits]

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

This is fine to me, I have some concerns about the out-of-bounds reads on the NumericLIteralParser, but if @cor3ntin and you have done the work to make sure it is ok, than I am ok with it.

https://github.com/llvm/llvm-project/pull/86586