Build host tools on non-FreeBSD host with DIRDEPS_BUILD

Add Makefile.depend.options to libnetbsd, mkimg and makefs
to ensure libegacy is build if needed.

targets/pseudo/stage/Makefile avoid the need for mtree
the staging process creates target dirs as needed anyway.

Reviewed by:	stevek
Sponsored by:	Juniper Networks, Inc.
Differential Revision:	https://reviews.freebsd.org/D39757

targets/pseudo/host-tools/Makefile

@@ -0,0 +1 @@
+.include "../Makefile.inc"

targets/pseudo/host-tools/Makefile.depend.host

@@ -0,0 +1,7 @@
+DIRDEPS= \
+        usr.bin/mkimg \
+        usr.bin/tar \
+        usr.sbin/makefs \
+
+.include <dirdeps.mk>
+

targets/pseudo/stage/Makefile

@@ -4,6 +4,7 @@
 # distrib-dirs can be done in STAGE_OBJTOP
 all:
 
+.if ${.MAKE.OS} == "FreeBSD"
 # mtree makes a lot of noise if we are not root, 
 # we don't need to see it.
 stage-distrib-dirs: .META ${META_DEPS}
@@ -11,6 +12,21 @@ stage-distrib-dirs: .META ${META_DEPS}
 	INSTALL="sh ${SRCTOP}/tools/install.sh" ${.MAKE} -C ${SRCTOP}/etc \
 	    distrib-dirs -DNO_FSCHG -DWITH_TESTS DESTDIR=${STAGE_OBJTOP}
 
+.else
+std_dirs= \
+	/bin \
+	/etc \
+	/sbin \
+	/usr/bin \
+	/usr/include/sys \
+	/usr/lib \
+	/usr/sbin \
+
+stage-distrib-dirs: .META
+	mkdir -p ${std_dirs:@d@${STAGE_OBJTOP}$d@}
+
+.endif
+
 .include <bsd.prog.mk>
 
 .if ${.MAKE.LEVEL} > 0 && ${MK_STAGING} == "yes"