Use -Werror in system/update_engine

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: Id9d961d4648de40c3d0ebc59ac6a2d1237d2d719
diff --git a/Android.mk b/Android.mk
index f02794c..54d45cc 100644
--- a/Android.mk
+++ b/Android.mk
@@ -82,6 +82,7 @@
 generated_sources_dir := $(call local-generated-sources-dir)
 LOCAL_EXPORT_C_INCLUDE_DIRS := $(generated_sources_dir)/proto/system
 LOCAL_SRC_FILES := $(ue_update_metadata_protos_src_files)
+LOCAL_CFLAGS := -Wall -Werror
 include $(BUILD_HOST_STATIC_LIBRARY)
 
 # Build for the target.
@@ -91,6 +92,7 @@
 generated_sources_dir := $(call local-generated-sources-dir)
 LOCAL_EXPORT_C_INCLUDE_DIRS := $(generated_sources_dir)/proto/system
 LOCAL_SRC_FILES := $(ue_update_metadata_protos_src_files)
+LOCAL_CFLAGS := -Wall -Werror
 include $(BUILD_STATIC_LIBRARY)
 
 # libpayload_consumer (type: static_library)