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

[Erich Keane via cfe-commits]

erichkeane 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.

Thanks!  This was really just a "tests would be a PITA to write, so lets restrict it and let someone who cares loosen it" situation, no real good reason otherwise.

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