Avoid failing in the backend when the rewrite map does not exist.  Rather check
that the map exists in the frontend before handing it off to the backend.  Add
the missing rewrite maps that the tests were referencing.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@282379 91177308-0d34-0410-b5e6-96231b3b80d8