expression to include the modifier.
- Gross, but this a corner case we don't expect to see often in practice, but
it is worth accepting.
- Also improves diagnostics on invalid modifiers.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114154 91177308-0d34-0410-b5e6-96231b3b80d8
