[clang] [clang] Fix PointerAuth semantics of cpp_trivially_relocatable (PR #143969)

[Corentin Jabot via cfe-commits]

cor3ntin wrote:

For people following at home, Oliver and I discussed this offline and we both agreed that enabling of relocation of discriminated vtable was a good first approach. we could always explore ways to extend what we support later, in a way that doesn't confuse people who try to relocate large arrays of discriminated pointers. The traits need to reflect what codegen supports, and Codegen should be worked on iteratively.

https://github.com/llvm/llvm-project/pull/143969