[llvm] [IR] Add llvm.masked.load.first.fault intrinsic (PR #156470)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

IIUC the new intrinsic has the same semantics as `llvm.vp.load.ff`, modulo the extra EVL argument?

If so, it would be nice if it would be possible to unify them if possible, not sure if we could have an optional EVL argument, which defaults to the number of elements of the vector type if omitted?

If that's not possible, it would be good to try to keep the names consistent (`load.ff` vs `load.first.fault`) and possibly share the wording for the  semantics definition somehow, possibly referencing `vp.load.ff`

https://github.com/llvm/llvm-project/pull/156470