[NFCI] Fix Wattributes warnings from Sema. (#157906)
See: https://github.com/llvm/llvm-project/issues/157834
There is some visibility concerns here, so this patch suppresses the
diagnostic. I believe we are doing this intentionally, so unless someone
comes up with a good reason we should either remove the visibility of
Sema, or make these types visible, this seems like the right way
forward.
Fixes: #157834
