[clang] [clang] Fix behavior of `__is_trivially_relocatable(volatile int)` (PR #77092)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

I think the changes make sense in as much as relocatable is supposed to be a subset of copyable (I continue to think `volatile`-qualified objects should not be trivially copyable... because they aren't... but that's WG21's issue, not ours).

I'm adding in the libc++ reviewers because this trait is used by libc++ and there's a potential for this to be an ABI-breaking change. I hope we don't need to add any ABI tags for this, but I wanted to give them a chance to weigh in.

https://github.com/llvm/llvm-project/pull/77092