[clang] [lld] [lld][LTO] Respect `-fno-slp-vectorize` for the LTO pipeline (PR #201585)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> Can this info be added to the IR e.g. a module flag or the like? Ideally we don't have to specially recognize every opt flag in the linker

I had that thought, but the current control is pretty much this, which means that adding a module flag would require some more invasive changes to how the pass functions because this level of config doesn't touch IR at all. I can try to add a function level attribute or similar for it and make the pass exit early if you think that's cleaner.
```c
if (Conf.SLPVectorize)
  addPass(SLPVectorize)
```

https://github.com/llvm/llvm-project/pull/201585