Include ARCH_FLAGS in CFLAGS when building modules.

Without this change, modules will match the default compiler
configuration which may not be the same as the kernel values.

Reviewed by:	imp
Obtained from:	CheriBSD
MFC after:	2 weeks
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D11633

sys/conf/kern.pre.mk

@@ -216,6 +216,7 @@ MKMODULESENV+=	MAKEOBJDIRPREFIX=${.OBJDIR}/modules KMODDIR=${KODIR}
 MKMODULESENV+=	MACHINE_CPUARCH=${MACHINE_CPUARCH}
 MKMODULESENV+=	MACHINE=${MACHINE} MACHINE_ARCH=${MACHINE_ARCH}
 MKMODULESENV+=	MODULES_EXTRA="${MODULES_EXTRA}" WITHOUT_MODULES="${WITHOUT_MODULES}"
+MKMODULESENV+=	ARCH_FLAGS="${ARCH_FLAGS}"
 .if (${KERN_IDENT} == LINT)
 MKMODULESENV+=	ALL_MODULES=LINT
 .endif

sys/conf/kmod.mk

@@ -366,7 +366,7 @@ ${_src}:
 .endif
 
 # Respect configuration-specific C flags.
-CFLAGS+=	${CONF_CFLAGS}
+CFLAGS+=	${ARCH_FLAGS} ${CONF_CFLAGS}
 
 .if !empty(SRCS:Mvnode_if.c)
 CLEANFILES+=	vnode_if.c