[clang] [clang] Update diagnostics to include matrices as accepted types (PR #201237)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Post-commit CI found relevant failures; can you fix or revert?

I'm not opposed to the changes that landed, but there doesn't seem to be any discussion of the fact that matrix types aren't enabled by default and so this diagnostic now talks about types the user may not even be able to spell. I would have expected we only mention matrix types if `-fenable-matrix` is passed. It's not the end of the world to always mention them; we're pretty inconsistent about how we mention extension types in diagnostics.

https://github.com/llvm/llvm-project/pull/201237