Don't use warning_as_errors for erlang.mk-style deps

Fix a bug where deps that use erlang.mk didn't have the -Werror
option suppressed automatically.

core/erlc.mk

@@ -93,7 +93,7 @@ erlc-include:
 	fi
 
 define compile_erl
-	$(erlc_verbose) erlc -v $(ERLC_OPTS) -o ebin/ \
+	$(erlc_verbose) erlc -v $(if $(IS_DEP),$(filter-out -Werror,$(ERLC_OPTS)),$(ERLC_OPTS)) -o ebin/ \
 		-pa ebin/ -I include/ $(filter-out $(ERLC_EXCLUDE_PATHS),\
 		$(COMPILE_FIRST_PATHS) $(1))
 endef

core/test.mk

@@ -20,7 +20,7 @@ ifneq ($(SKIP_DEPS),)
 test-deps:
 else
 test-deps: $(ALL_TEST_DEPS_DIRS)
-	$(verbose) for dep in $(ALL_TEST_DEPS_DIRS) ; do $(MAKE) -C $$dep; done
+	$(verbose) for dep in $(ALL_TEST_DEPS_DIRS) ; do $(MAKE) -C $$dep IS_DEP=1; done
 endif
 
 ifneq ($(wildcard $(TEST_DIR)),)