Test java/lang/ClassLoader/deadlock/TestCrossDelegate.sh is unable to find javac under Cygwin:

# set platform-specific variables
OS=`uname -s`
case "$OS" in
  SunOS )
    FS="/"
    ;;
  Linux )
    FS="/"
    ;;
  Windows* )
    FS="\\"
    ;;
esac

Under Cygwin 'uname -s' typically prints a string that begins with 'CYGWIN':

CYGWIN_NT-5.2-WOW64