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

[Lu Weining via cfe-commits]

SixWeining wrote:

> 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.

I'm not sure seperate PRs are appropriate since some of these 6 commits depend on the others. If creating 6 PRs, we will see:
PR1 consists of 1 commit
PR2 consists of 2 commits
...
PR6 consists of 6 commits

In fact, we can review each of these 6 commits in one PR by clicking the `Changes from all commits` button and `Select commit` in the `Files changed` tab.





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