[clang] [llvm] [LV][LAA] Vectorize math lib calls with mem write-only attribute (PR #78432)

[Paschalis Mpeis via cfe-commits]

paschalis-mpeis wrote:

### Rebased to:
1. Update to latest main
2. Amend commits for doing tests in veclib-function-calls.ll.

For (2), the commit history were modified as follows:
- The initial commit (that showcases what was missing) was amended to  add the tests in veclib-function-calls.ll.
- Then, subsequent commits were similarly amended to include the updates that allow vectorization.
- This currently latest commit simply dropped the no longer needed tests  (veclib-function-calls-linear-ptrs.ll)

https://github.com/llvm/llvm-project/pull/78432