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
(cherry picked from commit 7aa88748f6ec4e53333d1a15747bc44826ccc410)
diff --git a/Android.mk b/Android.mk
index 74910a1..1855623 100644
--- a/Android.mk
+++ b/Android.mk
@@ -65,7 +65,7 @@
 RECOVERY_API_VERSION := 3
 RECOVERY_FSTAB_VERSION := 2
 LOCAL_CFLAGS += -DRECOVERY_API_VERSION=$(RECOVERY_API_VERSION)
-LOCAL_CFLAGS += -Wno-unused-parameter
+LOCAL_CFLAGS += -Wno-unused-parameter -Werror
 LOCAL_CLANG := true
 
 LOCAL_C_INCLUDES += \
@@ -150,6 +150,7 @@
     verifier.cpp \
     ui.cpp
 LOCAL_STATIC_LIBRARIES := libcrypto_utils libcrypto libbase
+LOCAL_CFLAGS := -Werror
 include $(BUILD_STATIC_LIBRARY)
 
 include \