json-c: disable implicit fallthrough warning (gcc 7)

Signed-off-by: Felix Fietkau <[email protected]>

package/libs/libjson-c/Makefile

@@ -27,7 +27,7 @@ PKG_MAINTAINER:=Felix Fietkau <[email protected]>
 
 include $(INCLUDE_DIR)/package.mk
 
-TARGET_CFLAGS += $(FPIC)
+TARGET_CFLAGS += $(FPIC) -Wno-implicit-fallthrough
 
 define Package/libjson-c
   SECTION:=libs