知道了！
Java 1.8.45与ant 1.9.1不兼容. 切换到Java 1.7.67(jdk和jre)，一切运行正常.

Got it!!!
java 1.8.45 is not compatible with ant 1.9.1. Switched to java 1.7.67 (both jdk and jre) and everything is working fine.