Allow compatible extension attributes for tail calls

If the tail-callee and caller give the same bits via the same signext/zeroext
attribute then a tail-call should be allowed, since the extension has already
been done by the callee.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188159 91177308-0d34-0410-b5e6-96231b3b80d8