[clang] [Clang] Implement the core language parts of P2786 - Trivial relocation (PR #127636)

[Louis Dionne via cfe-commits]

https://github.com/ldionne commented:

I would like this patch to also deprecate the old builtin. I think the existence of the old builtin is going to cause significant confusion and risk introducing bugs. I always imagined that the old builtin would in fact be "fixed in place" once the Standard introduced the notion of TR, but I understand that introducing the Standard thing as a new name is probably better for backwards compatibility reasons. That being said, I would definitely want the old one to be deprecated with an explanation the very moment we introduce the new, Standards-conforming thing.

https://github.com/llvm/llvm-project/pull/127636