unconditionally check for goto correctness. This is because switch

statements don't end up in the LabelMap so we don't have a quick way
to filter them.  We could add state to Sema (a "has vla" and "has 
jump" bit) to try to filter this out, but that would be sort of gross
and I'm not convinced it is the best way.  Thoughts welcome.

llvm-svn: 69476