Use a macro variable PG_PRINTF_ATTRIBUTE for the style used for checking printf type...

Use a macro variable PG_PRINTF_ATTRIBUTE for the style used for checking printf type functions.

The style is set to "printf" for backwards compatibility everywhere except
on Windows, where it is set to "gnu_printf", which eliminates hundreds of
false error messages from modern versions of gcc arising from  %m and %ll{d,u}
formats.