[llvm] [LV] Teach the loop vectorizer llvm.sincos is trivially vectorizable (PR #128035)

[Benjamin Maxwell via llvm-commits]

MacDue wrote:

> One minor thing regarding the test file name. I think it is quite uncommon to use multiple `.` per file name (at least in the LoopVectorize subdirectory), using `-` or `_` would be more consistent with the existing naming.

I'll just remove the `llvm.` from the names

https://github.com/llvm/llvm-project/pull/128035