disable irrelevant openjdk target when openjdk is passed as a flag
Merge pull request #322 from joshuawarner32/ci-flexibility

disable irrelevant openjdk target when openjdk is passed as a flag
explicitly override UNUSED definition

Recent versions of jni.h such as the one provided by Debian Jessie's
OpenJDK define UNUSED in a way that conflicts with our definition and
usage, so we need to explicitly undefine it before redefining it to
avoid compiler noise.
Merge pull request #324 from dicej/unused

explicitly override UNUSED definition