[LoopVectorize] Fix VPRecipeBuilder::createEdgeMask to correctly generate the mask

This patch fixes pr48832 by correctly generating the mask when a poison value is involved.

Consider this CFG (which is a part of the input):

```
for.body:                                         ; preds = %for.cond
  br i1 true, label %cond.false, label %land.rhs

land.rhs:                                         ; preds = %for.body
  br i1 poison, label %cond.end, label %cond.false

cond.false:                                       ; preds = %for.body, %land.rhs
  br label %cond.end

cond.end:                                         ; preds = %land.rhs, %cond.false
  %cond = phi i32 [ 0, %cond.false ], [ 1, %land.rhs ]

```

The path for.body -> land.rhs -> cond.end should be taken when 'select i1 false, i1 poison, i1 false' holds (which means it's never taken); but VPRecipeBuilder::createEdgeMask was emitting 'and i1 false, poison' instead.
The former one successfully blocks poison propagation whereas the latter one doesn't, making the condition poison and thus causing the miscompilation.

SimplifyCFG has a similar bug (which didn't expose a real-world bug yet), and a patch for this is also ongoing (see https://reviews.llvm.org/D95026).

Reviewed By: bjope

Differential Revision: https://reviews.llvm.org/D95217