This is enabled by the undocumented option -fformat-extensions.
This option should be named better and/or give more control over
the extensions.
Fixed a message - don't warn about the field width when it's the
precision that has the wrong type. Didn't fix excessive checking
for the precision relative to the type - ANSI requires both to be
ints, but gcc permits the field width to be either int or unsigned
int.
f0825df278