Re-enable format string warnings on printf.
The warnings are still incomplete. Apparently it is undefined to use a
vector specifier without a length modifier, which is not currently
warned on. Additionally, type warnings appear to not be working with
the hh modifier, and aren't warning on all of the special restrictions
from c99 printf.
llvm-svn: 352540
The vector modifier is considered separate, so
don't treat it as a conversion specifier.
This is still not warning on some cases, like
using a type that isn't a valid vector element.
Fixes bug 39652
llvm-svn: 348084
Eric Liu