[NOT UPSTREAMABLE] checkpolicy: disable -Werror due to issues in flex…

…-generated code

This is a bug in flex 2.6.3:
westes/flex#155

lex.yy.c:397:0: error: "yywrap" redefined [-Werror]
lex.yy.c:73:0: note: this is the location of the previous definition

checkpolicy/Makefile

@@ -36,8 +36,8 @@ checkmodule: $(CHECKMODOBJS) $(LIBSEPOLA)
 y.tab.c: policy_parse.y
 	$(YACC) -d policy_parse.y
 
-# Disable warnings is code generated by flex 2.6.1
-lex.yy.o: CFLAGS += -Wno-error=sign-compare
+# Disable warnings in code generated by flex 2.6.1 and 2.6.3
+lex.yy.o: CFLAGS += -Wno-error
 
 lex.yy.c: policy_scan.l y.tab.c
 	$(LEX) policy_scan.l