[clang] [llvm] [LLVMABI] Align RecordType::isEmpty() with Clang's isEmptyRecord() (PR #218546)

[Adam Smith via cfe-commits]

https://github.com/adams381 approved this pull request.

I think the implementation looks good.  I think you are missing two test cases.

Can you add a unit test that omits the vptr field from the two virtual-base cases so `EmptyVBase` comes out true and `NonEmptyVBase` false?

Can you also add the `struct D : virtual B {}` case with `B` empty, which maps to a record with a virtual base and no vptr field, so that one comes out true?

https://github.com/llvm/llvm-project/pull/218546