Use -Werror in system/core/libnativebridge

* Fix unused static variable warning.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I9c3a2031ac49368a1833a9d46af8174c3c9cd32e
diff --git a/libnativebridge/tests/Android.mk b/libnativebridge/tests/Android.mk
index b3861e0..5b9ba1c 100644
--- a/libnativebridge/tests/Android.mk
+++ b/libnativebridge/tests/Android.mk
@@ -33,10 +33,15 @@
     libnativebridge \
     libnativebridge-dummy
 
+libnativebridge_tests_common_cflags := \
+    -Wall \
+    -Werror \
+
 $(foreach file,$(test_src_files), \
     $(eval include $(CLEAR_VARS)) \
     $(eval LOCAL_SHARED_LIBRARIES := $(shared_libraries)) \
     $(eval LOCAL_SRC_FILES := $(file)) \
+    $(eval LOCAL_CFLAGS := $(libnativebridge_tests_common_cflags)) \
     $(eval LOCAL_MODULE := $(notdir $(file:%.cpp=%))) \
     $(eval include $(BUILD_NATIVE_TEST)) \
 )
@@ -45,6 +50,7 @@
     $(eval include $(CLEAR_VARS)) \
     $(eval LOCAL_SHARED_LIBRARIES := $(shared_libraries)) \
     $(eval LOCAL_SRC_FILES := $(file)) \
+    $(eval LOCAL_CFLAGS := $(libnativebridge_tests_common_cflags)) \
     $(eval LOCAL_MODULE := $(notdir $(file:%.cpp=%))) \
     $(eval include $(BUILD_HOST_NATIVE_TEST)) \
 )