Add a kmod.opts.mk.

This Makefile sets KERN_OPTS.  This permits kernel module Makefiles to
use KERN_OPTS to control the value of variables such as SRCS that are
used by bsd.kmod.mk for KERN_OPTS values that honor WITH/WITHOUT
options for standalone builds.

share/mk/kmod.opts.mk

@@ -0,0 +1,4 @@
+# $FreeBSD$
+
+.include <bsd.sysdir.mk>
+.include "${SYSDIR}/conf/kmod.opts.mk"

sys/conf/kmod.mk

@@ -73,12 +73,7 @@ KMODUNLOAD?=	/sbin/kldunload
 KMODISLOADED?=	/sbin/kldstat -q -n
 OBJCOPY?=	objcopy
 
-.include <bsd.init.mk>
+.include "kmod.opts.mk"
-# Grab all the options for a kernel build. For backwards compat, we need to
-# do this after bsd.own.mk.
-.include "kern.opts.mk"
-.include <bsd.compiler.mk>
-.include "config.mk"
 .include <bsd.sysdir.mk>
 
 .SUFFIXES: .out .o .c .cc .cxx .C .y .l .s .S .m

sys/conf/kmod.opts.mk

@@ -0,0 +1,16 @@
+# $FreeBSD$
+#
+# Handle options (KERN_OPTS) for kernel module options.  This can be included earlier in a kmod Makefile
+# to allow KERN_OPTS to control SRCS, etc.
+
+.if !target(__<kmod.opts.mk>__)
+__<kmod.opts.mk>__:
+
+.include <bsd.init.mk>
+# Grab all the options for a kernel build. For backwards compat, we need to
+# do this after bsd.own.mk.
+.include "kern.opts.mk"
+.include <bsd.compiler.mk>
+.include "config.mk"
+
+.endif #  !target(__<kmod.opts.mk>__)