[clang] [Clang][LoongArch] Support builtin functions for LSX and LASX (PR #69313)

[WÁNG Xuěruì via cfe-commits]

xen0n wrote:

According to [the *LLVM GitHub user guide*](https://llvm.org/docs/GitHub.html#creating-pull-requests):

> If you have multiple changes you want to introduce, it’s recommended to create separate pull requests for each change.

Given you've already split your changes into several smaller commits, it's probably better to file them as separate PRs, so each one is smaller than the current 30000+-line diff, and become more reviewable that way.

https://github.com/llvm/llvm-project/pull/69313