[ScalarEvolutionExpander] PHI on a catchpad can be used on both edges

[ScalarEvolutionExpander] PHI on a catchpad can be used on both edges

A PHI on a catchpad might be used by both edges out of the catchpad,
feeding back into a loop.  In this case, just use the insertion point.
Anything more clever would require new basic blocks or PHI placement.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251442 91177308-0d34-0410-b5e6-96231b3b80d8