[LoopStrengthReduce] Don't rewrite PHIs with incoming values from CatchSwitches

Bail out if we have a PHI on an EHPad that gets a value from a
CatchSwitchInst.  Because the CatchSwitchInst cannot be split, there is
no good place to stick any instructions.

This fixes PR26373.

llvm-svn: 259702
3 files changed