Turn on -Werror for recovery

Also remove the 0xff comparison when validating the bootloader
message fields. As the fields won't be erased to 0xff after we
remove the MTD support.

Bug: 28202046
Test: The recovery folder compiles for aosp_x86-eng
Change-Id: Ibb30ea1b2b28676fb08c7e92a1e5f7b6ef3247ab
diff --git a/update_verifier/Android.mk b/update_verifier/Android.mk
index ed61c7b..8f5194d 100644
--- a/update_verifier/Android.mk
+++ b/update_verifier/Android.mk
@@ -20,5 +20,6 @@
 LOCAL_SRC_FILES := update_verifier.cpp
 LOCAL_MODULE := update_verifier
 LOCAL_SHARED_LIBRARIES := libhardware libbase
+LOCAL_CFLAGS := -Werror
 
 include $(BUILD_EXECUTABLE)