Import NetBSD tools and build.sh

This commit finalizes support for cross compilation. The tools
directory are all links to the actual tools and are built on the
host system to build Minix. build.sh is the work horse that takes
care of all environment settings. It's slightly adjusted for Minix.
The /usr/src/Makefile has additional targets needed for cross
compilation.

tools/Makefile.gmakehost

@@ -0,0 +1,21 @@
+#	$NetBSD: Makefile.gmakehost,v 1.7 2012/01/20 23:01:05 christos Exp $
+#
+# Rules used when building a GNU host package.  Expects MODULE to be set.
+# This version runs ${TOOL_GMAKE} instead of ${MAKE}
+#
+# There's not a lot we can do to build reliably in the face of many
+# available configuration options.  To be as low-overhead as possible,
+# we follow the following scheme:
+#
+# * Configuration is only re-run when an autoconf source file (such as
+#   "configure" or "config.sub") is changed.
+#
+# * "config.status" is run to rebuild Makefiles and .h files if an
+#   autoconf-parsed file (such as Makefile.in) is changed.
+#
+# * If MKUPDATE != "no", "make install" is only run if a build has happened
+#   since the last install in the current directory.
+
+.include <bsd.own.mk>
+MAKE_PROGRAM=${TOOL_GMAKE}
+.include "Makefile.gnuhost"