[clang] [Clang] Allow vector and matrix type attributes for sub-byte _BitInt (PR #140253)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I don't have a problem with this, but I'd need to see a LOT more tests here.  We have this restriction because it wasn't clear whether the semantics work correctly for codegen/llvm backends.

So I'd need to see some codegen tests that show that we're doing the right thing for these, plus some sort of testing that shows that we do the right thing with llvm codegen.

https://github.com/llvm/llvm-project/pull/140253