Kernels modules are c99 (gnu99) just like the kernel.

Add(move) -std=gnu99 to CPPFLAGS (from COPTS).

share/mk/bsd.kmodule.mk

@@ -1,4 +1,4 @@
-#	$NetBSD: bsd.kmodule.mk,v 1.26 2010/12/11 18:42:33 martin Exp $
+#	$NetBSD: bsd.kmodule.mk,v 1.27 2011/01/02 19:24:47 matt Exp $
 
 # We are not building this with PIE
 MKPIE=no
@@ -17,6 +17,7 @@ CFLAGS+=	-ffreestanding ${COPTS}
 CPPFLAGS+=	-nostdinc -I. -I${.CURDIR} -isystem $S -isystem $S/arch
 CPPFLAGS+=	-isystem ${S}/../common/include
 CPPFLAGS+=	-D_KERNEL -D_LKM -D_MODULE
+CPPFLAGS+=	-std=gnu99
 
 # XXX until the kernel is fixed again...
 .if (defined(HAVE_GCC) && ${HAVE_GCC} == 4) || defined(HAVE_PCC)

sys/conf/Makefile.kern.inc

@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile.kern.inc,v 1.127 2010/03/05 23:06:49 njoly Exp $
+#	$NetBSD: Makefile.kern.inc,v 1.128 2011/01/02 19:24:48 matt Exp $
 #
 # This file contains common `MI' targets and definitions and it is included
 # at the bottom of each `MD' ${MACHINE}/conf/Makefile.${MACHINE}.
@@ -57,9 +57,9 @@ S!=	cd ../../../..; pwd
 INCLUDES?=	-I. ${EXTRA_INCLUDES} -I${S}/../common/include -I$S/arch \
 		-I$S -nostdinc
 CPPFLAGS+=	${INCLUDES} ${IDENT} ${PARAM} -D_KERNEL -D_KERNEL_OPT
+CPPFLAGS+=	-std=gnu99
 DEFCOPTS?=	-O2
 COPTS?=		${DEFCOPTS}
-COPTS+=		-std=gnu99
 DBG=		# might contain unwanted -Ofoo
 DEFWARNINGS?=	yes
 .if (${DEFWARNINGS} == "yes")