TRE: make TRE a bit more aggressive

Make tail recursion elimination a bit more aggressive.  This allows us to get
tail recursion on functions that are just branches to a different function.  The
fact that the function takes a byval argument does not restrict it from being
optimised into just a tail call.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219899 91177308-0d34-0410-b5e6-96231b3b80d8