include/linux/compat.h: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases where
we are expecting to fall through.

Link: http://lkml.kernel.org/r/20181013115048.GA3262@embeddedor.com
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/compat.h

@@ -488,8 +488,11 @@ put_compat_sigset(compat_sigset_t __user *compat, const sigset_t *set,
 	compat_sigset_t v;
 	switch (_NSIG_WORDS) {
 	case 4: v.sig[7] = (set->sig[3] >> 32); v.sig[6] = set->sig[3];
+		/* fall through */
 	case 3: v.sig[5] = (set->sig[2] >> 32); v.sig[4] = set->sig[2];
+		/* fall through */
 	case 2: v.sig[3] = (set->sig[1] >> 32); v.sig[2] = set->sig[1];
+		/* fall through */
 	case 1: v.sig[1] = (set->sig[0] >> 32); v.sig[0] = set->sig[0];
 	}
 	return copy_to_user(compat, &v, size) ? -EFAULT : 0;