[clang] [flang] [flang] Add -f[no-]slp-vectorize flags (PR #132801)

[Kajetan Puchalski via cfe-commits]

mrkajetanp wrote:

> If you are soliciting reviews, you could also use the "Reviewers" box on the top right of this page

I would, but I do not currently have the right permissions to use the box. Hence the ccs - I need someone else to do it. 

https://github.com/llvm/llvm-project/pull/132801