do the Makefile checking using make itself

sys/unix/hints/linux.370

@@ -17,11 +17,10 @@
 # as Ubuntu focal).
 
 # note: '#-INCLUDE' is not just a comment
-#
-#-INCLUDE general-pre.370
 #        multiw-1.370 contains sections 1 to 2
 #-INCLUDE multiw-1.370
 
+PRECHECK+=checkmakefiles
 
 ifndef LIBXPM
 LIBXPM= -L/opt/X11/lib -lXpm
@@ -360,6 +359,10 @@ GAMEPERM = 0755
 #-INCLUDE multisnd-post.370
 #
 
+.PHONY: checkmakefiles
+checkmakefiles:
+	( $(MAKE) -f sys/unix/Makefile.check )
+
 ifdef WANT_LIBNH
 $(TARGETPFX)libnh.a: $(HOBJ) $(LIBNHSYSOBJ) ../lib/lua/liblua.a
 	$(AR) rcs $@ $(HOBJ) $(LIBNHSYSOBJ) ../lib/lua/liblua.a