[clang] [Clang] Implement diagnostics for why `std::is_standard_layout` is false (PR #144161)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @AaronBallman, as per the comment I left below: it is because of the conflicting definitions of the TableGen description of `VirtualFunction`. Will push a resolution soon.
> 
> > Needs some manual intervention after the merge. Conflicting redundance in the tablegen descriptions of `VirtualFunction`
> 
> (This creeped in because of the `is_empty` PR I merged earlier in the day :))

Oops! I thought you were talking about merge conflicts. :-)

https://github.com/llvm/llvm-project/pull/144161