unbreak make includes on non-clang archs after libobjc removal

found the hard way by nayden@ ok deraadt@

src/include/Makefile

@@ -1,4 +1,4 @@
-#	$OpenBSD: Makefile,v 1.224 2019/03/05 09:44:38 jsg Exp $
+#	$OpenBSD: Makefile,v 1.225 2019/04/06 02:56:16 jsg Exp $
 #	$NetBSD: Makefile,v 1.59 1996/05/15 21:36:43 jtc Exp $
 
 #	@(#)Makefile	5.45.1.1 (Berkeley) 5/6/91
@@ -53,11 +53,10 @@ RDIRS=	../lib/libcurses ../lib/libedit ../lib/libelf \
 	../sys/arch/${MACHINE}
 
 .if ${BUILD_GCC3:L} == "yes"
-RDIRS+= ../gnu/usr.bin/gcc ../gnu/lib/libobjc
+RDIRS+= ../gnu/usr.bin/gcc
 PRDIRS+= ../gnu/lib/libstdc++
 .endif
 .if ${BUILD_GCC4:L} == "yes"
-RDIRS+= ../gnu/usr.bin/cc/libobjc
 PRDIRS+= ../gnu/lib/libstdc++-v3 ../gnu/usr.bin/cc/include
 .endif
 .if ${BUILD_CLANG:L} == "yes"