Fix the location of "missing ';'" suggestions after annotation tokens.

We were incorrectly setting PrevTokLocation to the first token in the
annotation token instead of the last when consuming it. To fix this without
adding a complex switch to the hot path through ConsumeToken, we now have a
ConsumeAnnotationToken function for consuming annotation tokens in addition
to the other Consume*Token special case functions.

llvm-svn: 303372