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

[Kajetan Puchalski via cfe-commits]

mrkajetanp wrote:

> Apart from the docstrings, this looks good. Thanks for the changes :-)

Done, thanks a lot for the review! :) 

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