[ScalarEvolutionExpander] Properly insert no-op casts + EH Pads

[ScalarEvolutionExpander] Properly insert no-op casts + EH Pads

We want to insert no-op casts as close as possible to the def.  This is
tricky when the cast is of a PHI node and the BasicBlocks between the
def and the use cannot hold any instructions.  Iteratively walk EH pads
until we hit a non-EH pad.

This fixes PR25326.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251393 91177308-0d34-0410-b5e6-96231b3b80d8