Stop looking up these values in every subdir on install.

This was slowing down installkernel since it was rerunning this in
every module directory.

Sponsored by:	EMC / Isilon Storage Division

sys/conf/config.mk

@@ -49,6 +49,7 @@ KERN_OPTS+= INET6
 .if ${MK_EISA} != "no"
 KERN_OPTS+= DEV_EISA
 .endif
-.else
+.elif !defined(KERN_OPTS)
 KERN_OPTS!=cat ${KERNBUILDDIR}/opt*.h | awk '{print $$2;}' | sort -u
+.export KERN_OPTS
 .endif

sys/conf/kern.opts.mk

@@ -144,7 +144,10 @@ MK_${var}:=	no
 MK_${var}_SUPPORT:= no
 .else
 .if defined(KERNBUILDDIR)	# See if there's an opt_foo.h
+.if !defined(OPT_${var})
 OPT_${var}!= cat ${KERNBUILDDIR}/opt_${var:tl}.h; echo
+.export OPT_${var}
+.endif
 .if ${OPT_${var}} == ""		# nothing -> no
 MK_${var}_SUPPORT:= no
 .else