x32: fix waitid()

It needs 64bit rusage and 32bit siginfo.  glibc never calls it with
non-NULL rusage pointer, or we would've seen breakage already...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/compat.c

@@ -587,6 +587,10 @@ COMPAT_SYSCALL_DEFINE5(waitid,
 		return ret;
 
 	if (uru) {
+		/* sys_waitid() overwrites everything in ru */
+		if (COMPAT_USE_64BIT_TIME)
+			ret = copy_to_user(uru, &ru, sizeof(ru));
+		else
 			ret = put_compat_rusage(&ru, uru);
 		if (ret)
 			return ret;