buildsystem: Promote rules.h to default include

Does not fix 3rdparty/, *.S or *.ld or yet.

Change-Id: I66b48013dd89540b35ab219d2b64bc13f5f19cda
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/17656
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/include/stddef.h

@@ -2,7 +2,6 @@
 #define STDDEF_H
 
 #include <commonlib/helpers.h>
-#include <rules.h>
 
 typedef long ptrdiff_t;
 #ifndef __SIZE_TYPE__