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

[Dmitry Sidorov via cfe-commits]

MrSidims wrote:

@erichkeane @AaronBallman please take a look. Limitation that currently clang has seem to be unreasonable. Currently I'm just removing it, but I'm open to introducing a flag, that suppresses the error or make this error be a warning.

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