InstrProf: Handle whitespace and comments at the ends of macros

When we try to find the end loc for a token, we have to re-lex the
token. This was running into a problem when we'd store the end loc of
a macro's coverage region, since we wouldn't actually be at the
beginning of a token when we tried to re-lex it, leading us to do
silly things (and eventually assert) when whitespace or comments
followed.

This pushes our use of getPreciseTokenLocEnd earlier, so that we won't
call it when it doesn't make sense to. It also removes an unnecessary
adjustment by 1 that was working around this problem in some cases.

llvm-svn: 233169