Patch by Cristian Draghici:

Enhance the printf format string checking when using the format
specifier flags ' ', '0', '+' with the 'p' or 's' conversions (since
they are nonsensical and undefined).  This is similar to GCC's
checking.

Also warning when a precision is used with the 'p' conversin
specifier, since it has no meaning.

llvm-svn: 95869