$ cat | gcc-5 -x c - -c -o /dev/null -Wformat=2
#include <stdio.h>

void x(unsigned short arg)
{
        printf("%x\n", arg);
}
^D
gives:
<stdin>: In function ���x���:
<stdin>:5:16: warning: format ���%x��� expects argument of type ���unsigned int���, but
argument 2 has type ���int��� [-Wformat=]