Use format(gnu_printf, ...) for windows build with __USE_MINGW_ANSI_STDIO

With __USE_MINGW_ANSI_STDIO mingw compiler uses its own replacement
printf*/scanf* libraries instead of Microsoft's ones which aren't always
C99 compatible.  Declare "archetype" of attribute format to gnu_printf
because the default "printf" in mingw follows MS standard.

One result is that "%z" (a gnu-extension) is accepted w/o warning by
mingw compiler

Change-Id: I3e92f34e2a1e8d664b4f1f55d450f7c2790671f3