Use ln -n instead of -h to allow building the kernel on Linux

Both flags do the same thing but -n is more widely supported.

Reviewed By:	jhb, emaste
Approved By:	jhb (mentor)
Differential Revision: https://reviews.freebsd.org/D13936

sys/conf/kern.post.mk

@@ -300,7 +300,7 @@ ${_ILINKS}:
 		path=${S}/${.TARGET}/include ;; \
 	esac ; \
 	${ECHO} ${.TARGET} "->" $$path ; \
-	ln -fhs $$path ${.TARGET}
+	ln -fns $$path ${.TARGET}
 
 # .depend needs include links so we remove them only together.
 kernel-cleandepend: .PHONY

sys/conf/kmod.mk

@@ -292,7 +292,7 @@ ${_ILINKS}:
 	esac ; \
 	path=`(cd $$path && /bin/pwd)` ; \
 	${ECHO} ${.TARGET:T} "->" $$path ; \
-	ln -fhs $$path ${.TARGET:T}
+	ln -fns $$path ${.TARGET:T}
 
 CLEANFILES+= ${PROG} ${KMOD}.kld ${OBJS}