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

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Sirraide wrote:

> The type of an alloca is only used to determine the number of bytes allocated;

Yeah, that part I know; I was mainly just wondering if there’s a platform/abi/whatever where that doesn’t work out.

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