Fix build: ignore a GCC 7.2.0 warning which says that third argument of

memset(3) should contain the number of elements multiplied by the element
size.

Sponsored by:	DARPA, AFRL

sys/conf/kern.mk

@@ -67,6 +67,9 @@ CWARNEXTRA+=	-Wno-error=misleading-indentation		\
 		-Wno-error=shift-overflow			\
 		-Wno-error=tautological-compare
 .endif
+.if ${COMPILER_VERSION} >= 70200
+CWARNEXTRA+=	-Wno-error=memset-elt-size
+.endif
 .if ${COMPILER_VERSION} >= 80000
 CWARNEXTRA+=	-Wno-error=packed-not-aligned
 .endif