[clang] Patch series to reapply #118734 and substantially improve it (PR #120534)

[Phoebe Wang via cfe-commits]

phoebewang wrote:

> I proposed this at one point, and someone from Intel assured me that these long repetitive instructions and intrinsics are hand-maintained. It must be true at some level.

I believe it's not me, though I don't like the changes at the beginning either. Anyway, with @chandlerc 's great script, we have migrated our internal bultins. Hope this won't affect them much.

https://github.com/llvm/llvm-project/pull/120534