Per https://github.com/ReadyTalk/avian/issues/53, Avian should build
against a standard AOSP checkout, which means we should look for
subprojects in the directories the repo utility would place them.
With corresponding changes to libcore, all the tests are passing
except Datagrams, which fails with a NPE in
NetworkInterface.getNetworkInterfacesList due to OS X not having
/sys/class/net. Porting that class to OS X looks like a non-trivial
task.
