In this log: https://tbpl.mozilla.org/php/getParsedLog.php?id=9300043&tree=Try&full=1 an 'rm -r' command fails, saying: rm: WARNING: Circular directory structure. This almost certainly means that you have a corrupted file system. NOTIFY YOUR SYSTEM MANAGER. The following directory is part of the cycle: `build/.hg/store/data/mobile/android/config'
That message is usually the result of msys not quite understanding how NTFS works, and it self corrects, but I've blown away the dir anyway.