[IR] Give catchret an optional 'return value' operand

[IR] Give catchret an optional 'return value' operand

Some personality routines require funclet exit points to be clearly
marked, this is done by producing a token at the funclet pad and
consuming it at the corresponding ret instruction.  CleanupReturnInst
already had a spot for this operand but CatchReturnInst did not.
Other personality routines don't need to use this which is why it has
been made optional.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245149 91177308-0d34-0410-b5e6-96231b3b80d8