[clang] [Clang] [Sema] Reject non-power-of-2 `_BitInt` matrix element types (PR #117487)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> > an integer type (as in C23 6.2.5p22)
> 
> Doesn’t 6.2.5p22 include 6.2.5.p5 i.e. `_BitInt`s?
> 
> CC @AaronBallman

That's correct, `_BitInt` is an `integer type` in C's words of power.

https://github.com/llvm/llvm-project/pull/117487