Index: sys/conf/kern.opts.mk
===================================================================
--- sys/conf/kern.opts.mk
+++ sys/conf/kern.opts.mk
@@ -60,7 +60,8 @@
     INIT_ALL_ZERO \
     KERNEL_RETPOLINE \
     RATELIMIT \
-    REPRODUCIBLE_BUILD
+    REPRODUCIBLE_BUILD \
+    SET_NOTUSED_MODULE_WARNINGS
 
 # Some options are totally broken on some architectures. We disable
 # them. If you need to enable them on an experimental basis, you
Index: sys/conf/kmod.mk
===================================================================
--- sys/conf/kmod.mk
+++ sys/conf/kmod.mk
@@ -115,6 +115,10 @@
 CFLAGS+=	-DKLD_TIED
 .endif
 
+.if ${MK_SET_NOTUSED_MODULE_WARNINGS} == "no"
+CWARNEXTRA+=	${NO_WUNUSED_BUT_SET_VARIABLE}
+.endif
+
 # Don't use any standard or source-relative include directories.
 NOSTDINC=	-nostdinc
 CFLAGS:=	${CFLAGS:N-I*} ${NOSTDINC} ${INCLMAGIC} ${CFLAGS:M-I*}