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/minui/Android.mk b/minui/Android.mk
index 380ec2b..67b81fc 100644
--- a/minui/Android.mk
+++ b/minui/Android.mk
@@ -13,6 +13,7 @@
 LOCAL_WHOLE_STATIC_LIBRARIES += libdrm
 LOCAL_WHOLE_STATIC_LIBRARIES += libsync_recovery
 LOCAL_STATIC_LIBRARIES += libpng
+LOCAL_CFLAGS := -Werror
 
 LOCAL_MODULE := libminui
 
@@ -46,4 +47,5 @@
 LOCAL_MODULE := libminui
 LOCAL_WHOLE_STATIC_LIBRARIES += libminui
 LOCAL_SHARED_LIBRARIES := libpng
+LOCAL_CFLAGS := -Werror
 include $(BUILD_SHARED_LIBRARY)