AU: Include a bit flag (bit 31) in error codes to indicate non-normal boot mode.

BUG=chromium-os:10320
TEST=unit test, tested on device in normal and dev mode

Change-Id: I67d695bc167a4cc1a638711f047e2b86f8eaa8f1

Review URL: http://codereview.chromium.org/6098008
diff --git a/SConstruct b/SConstruct
index 615d18c..f75b256 100644
--- a/SConstruct
+++ b/SConstruct
@@ -195,6 +195,7 @@
 
 env['LIBS'] = Split("""base
                        bz2
+                       cros_boot_mode
                        crypto
                        curl
                        ext2fs