Add JarJar support to BUILD_HOST_JAVA_LIBRARY

This will allow us to convert icu4j-icudata / icu4j-icutzdata
targets to "host" targets rather than "target" targets.
Right now they are forcing Jack off just so they can use
javac + jarjar (even though the resulting file is used on
host).

Bug: 27218410
Change-Id: I7062c698389d98b0dde5690280a9140c3b12cbf7