Re-add MKTOOLS as a "yes"/"no" only variable, which prevents recursion on "no"

into the src/tools subdirs on all/depend/dependall/install.  Other recursive
targets are not affected.

tools/Makefile

@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile,v 1.16 2001/11/12 23:16:22 tv Exp $
+#	$NetBSD: Makefile,v 1.17 2001/11/13 16:17:24 tv Exp $
 
 .include <bsd.own.mk>
 
@@ -16,6 +16,20 @@ SUBDIR=	mkdep .WAIT \
 		asn1_compile compile_et config lint1 msgc menuc mklocale
 .endif
 
+.if ${MKTOOLS:Uyes} == "no"
+realall install: _warn
+_warn:
+	@echo '*** WARNING: "MKTOOLS" is set to "no"; this will prevent building and'
+	@echo '*** updating your host toolchain.  This should be used only as a'
+	@echo '*** temporary workaround for toolchain problems, as it will result'
+	@echo '*** in version skew and build errors onver time!'
+
+.for dir in ${SUBDIR:N.WAIT}
+all-${dir} depend-${dir} dependall-${dir} install-${dir}:
+	@true
+.endfor
+.endif
+
 .include <bsd.subdir.mk>
 .include <bsd.obj.mk>