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

[Dmitry Sidorov via cfe-commits]

MrSidims wrote:

> 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.

Sure, I'll work on this.

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