vfprintf-posix: Use vfzprintf. * lib/stdio.in.h (vfprintf): Add specification. * lib/vfprintf.c: Don't include <stdlib.h>, vasnprintf.h. Include intprops.h. (vfprintf): Implement based on vfzprintf. * modules/vfprintf-posix (Depends-on): Add vfzprintf, intprops. Remove vasnprintf, free-posix.