Try to avoid all files dependence on the modification time of the large and

often modified directory created symbolic links points to - it cause
unnecessary full rebuilds each time make runs when directory is changed.
So do it only if symbolic link does not exists, which usually means that
objdir is clean anyway.

MFC after:      1 week

sys/boot/ficl/Makefile

@@ -54,9 +54,11 @@ softcore.c: ${SOFTWORDS} softcore.awk
 	    | awk -f softcore.awk -v datestamp="`LC_ALL=C date`") > ${.TARGET}
 
 .if ${MACHINE_CPUARCH} == "amd64"
+.if !exists(machine)
 ${SRCS:M*.c:R:S/$/.o/g}: machine
 
 beforedepend ${OBJS}: machine
+.endif
 
 machine:
 	ln -sf ${.CURDIR}/../../i386/include machine

sys/boot/zfs/Makefile

@@ -33,5 +33,7 @@ machine:
 .include <bsd.lib.mk>
 
 .if ${MACHINE_CPUARCH} == "amd64"
+.if !exists(machine)
 beforedepend ${OBJS}: machine
 .endif
+.endif