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

[Kajetan Puchalski via cfe-commits]

mrkajetanp wrote:

> Is this buildbot failure related: [https://lab.llvm.org/buildbot/#/builders/89/builds/19482](https://lab.llvm.org/buildbot/#/builders/89/builds/19482)?

Ah yes, sorry about that! Just a missing -o /dev/null, I'll post a fix in a moment. 

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