[llvm] [GVN] Add MemorySSA checks in tests 1/N (PR #130261)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> > This looks reasonable to me now. @antoniofrighetto Any concerns with testing MSSA? Also, do you think it would make sense to make `gvn<memoryssa>` work by having it imply `no-memdep`?
> 
> I second this. Either of them will be in use, so enabling one should imply the disablement of the other.

That makes sense. I think it would be ideal to do this after flipping the flag.

https://github.com/llvm/llvm-project/pull/130261