Teach this to create the "machine" and ${MACHINE_ARCH} (for pc98

only now) symbolic links in the kernel compile directory, rather
than relying on config(8) to do this.  (The changes to config(8)
will be committed separately.)  This is aimed towards making the
config(8) as lightweight as possible.

Idea by:	bde (all bugs are mine)

sys/conf/kern.post.mk

@@ -112,7 +112,7 @@ kernel-clean:
 	    linterrs makelinks tags vers.c \
 	    vnode_if.c vnode_if.h vnode_if_newproto.h vnode_if_typedef.h \
 	    ${MFILES:T:S/.m$/.c/} ${MFILES:T:S/.m$/.h/} \
-	    ${CLEAN}
+	    ${CLEAN} ${_ILINKS}
 
 lint: ${LNFILES}
 	${LINT} ${LINTKERNFLAGS} ${CFLAGS:M-[DILU]*} ${.ALLSRC} 2>&1 | \
@@ -141,9 +141,10 @@ ${SYSTEM_OBJS} genassym.o vers.o: opt_global.h
 kernel-depend: .depend
 # The argument list can be very long, so use make -V and xargs to
 # pass it to mkdep.
-.depend: assym.s vnode_if.h ${BEFORE_DEPEND} ${CFILES} \
-	    ${SYSTEM_CFILES} ${GEN_CFILES} ${SFILES} \
-	    ${MFILES:T:S/.m$/.h/}
+SRCS=	assym.s vnode_if.h ${BEFORE_DEPEND} ${CFILES} \
+	${SYSTEM_CFILES} ${GEN_CFILES} ${SFILES} \
+	${MFILES:T:S/.m$/.h/}
+.depend: ${SRCS}
 	rm -f .newdep
 	${MAKE} -V CFILES -V SYSTEM_CFILES -V GEN_CFILES | \
 	    MKDEP_CPP="${CC} -E" CC="${CC}" xargs mkdep -a -f .newdep ${CFLAGS}
@@ -152,6 +153,28 @@ kernel-depend: .depend
 	rm -f .depend
 	mv .newdep .depend
 
+_ILINKS= machine
+.if ${MACHINE} != ${MACHINE_ARCH}
+_ILINKS+= ${MACHINE_ARCH}
+.endif
+
+# Ensure that the link exists without depending on it when it exists.
+.for _link in ${_ILINKS}
+.if !exists(${.OBJDIR}/${_link})
+${SRCS}: ${_link}
+.endif
+.endfor
+
+${_ILINKS}:
+	@case ${.TARGET} in \
+	machine) \
+		path=${S}/${MACHINE}/include ;; \
+	${MACHINE_ARCH}) \
+		path=${S}/${MACHINE_ARCH}/include ;; \
+	esac ; \
+	${ECHO} ${.TARGET} "->" $$path ; \
+	ln -s $$path ${.TARGET}
+
 kernel-cleandepend:
 	rm -f .depend