Experimental support for jack on host mode.
This includes adding a --toolchain={jack,jdk} option which chooses what
to compile sources with. Currently only works with host mode and pending
on b/22382563 to be able to properly compile code with dependencies on
the surrounding package. This depends on the prebuilt jack jar file in

Change-Id: Id4d5eaa51318009fd8a147e4c548be3c62f9c5aa
7 files changed