[clang] [clang][Sema] Track trivial-relocatability as a type trait (PR #84621)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> Do you mean that you would reject a proposal that adds Clang-specific trait (with another name) that implements P1144's semantics?

So long as it checks all the boxes in our usual [criteria](https://clang.llvm.org/get_involved.html#criteria) for extensions, I'd see no reason to oppose additional type traits. However, the push back right now comes from point #4: the idea was proposed to a standards body and that idea was rejected. So long as whatever new idea comes along has some chance of standardization, then it would be reasonable to add. If the trait was also supported in GCC, that would also help build a case for including it in Clang.

https://github.com/llvm/llvm-project/pull/84621