[clang] [clang][CodeGen] Fix metadata when vectorization is disabled by pragma (PR #135163)

[Ryotaro Kasuga via cfe-commits]

kasuga-fj wrote:

> Unfortuantely IIRC there is a semantic difference between pragma and metadata:
>
>    - llvm.loop.vectorize.enable==false disables vectorization AND interleaving (by switching off the entire LoopVectorize pass which does both of thise things)
>    - llvm.loop.vectorize.width==1 disables vectorization, but still permits interlaving
>    - llvm.loop.interleave.count==1 should disable interleaving but still permit vectorization

I see, I got it, thanks.

> I think the correct logic should detect that "llvm.loop.vectorize.width==1" means off, and like that add the unroll to the metadata node itself, instead its followup.

Given the above facts, I also think this approach is reasonable. Thanks, I will try in this way.

https://github.com/llvm/llvm-project/pull/135163