[clang] [clang][Builtins] Parse clang extended vectors types. (PR #83584)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

Hm, yeah. I don't think it's worth complicating the parser for a tiny bit of syntax sugar. I like your idea with a `:` quite a bit. `_ExtVector(bool:4)` would also be an option. I don't have a strong preference either way. I'd like to keep it separate from the name though to make it obvious that it's a parameter (at least it feels to me like that).

https://github.com/llvm/llvm-project/pull/83584