Handle the case of a tail recursion in which the tail call is followed

Handle the case of a tail recursion in which the tail call is followed
by a return that returns a constant, while elsewhere in the function
another return instruction returns a different constant.  This is a
special case of accumulator recursion, so just generalize the existing
logic a bit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108241 91177308-0d34-0410-b5e6-96231b3b80d8