Replace hardcoded 11 with a define

The 11 comes from the legacy API that we need to be binary compatible with.
Make this clear with a define and a comment.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Fix compiler warning - implicit declaration of function 'abs'

match_four.c:80:4: warning: implicit declaration of function 'abs'
[-Wimplicit-function-declaration]
    *dist++ = abs(q->x - p->x) + abs(q->y - p->y);

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
test: silence compiler warning - implicit declaration of function ‘atoi’

mtdev-kernel.c:130:2: warning: implicit declaration of function ‘atoi’
[-Wimplicit-function-declaration]
  eslot = atoi(argv[1]) + 1;

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Enable silent rules by default

silent rules make it easier to spot compiler errors

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>