Add default -Werror to system/vold/tests.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I730943ace4aa329459d6280d1c2be601f7383343
diff --git a/cc/config/global.go b/cc/config/global.go
index a3d2b04..5d1f7c4 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -138,7 +138,6 @@
 		"hardware/libhardware/modules/",
 		"hardware/qcom/",
 		"sdk/emulator/mksdcard/",
-		"system/vold/tests/",
 		"tools/adt/idea/android/ultimate/get_modification_time/jni/",
 	}
 )