[clang] [C23] Implement WG14 N3037 (PR #132939)

[Martin Uecker via cfe-commits]

uecker wrote:

BTW: I did not push for this feature to be exposed in earlier language modes because GCC will ship with GNU C23 by default with GCC 15.   GCC 15 already saw distribution-wide testing in Redhat and Debian and from this experience I do not expect any problems related to this feature (so far, I am not aware of any issue caused by this feature, which can not be said about some other C23 changes).  Unrelated testing exercising the new features uncovered a couple of bugs in my implementation (as well as other unrelated bugs in GCC), and I would expect that this will be true for Clang as well. But I would not expect anything critical.  

https://github.com/llvm/llvm-project/pull/132939