[CodeGenPrepare] Teach the addressing mode matcher how to promote zext.
I.e., teach it about 'sext (zext a to ty) to ty2' => zext a to ty2.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217629 91177308-0d34-0410-b5e6-96231b3b80d8