The current hotspot makefiles have dummy targets which indicate <how>
rather than <what> to build. This was a convience when there was only
one target to be built.

The makefiles should support multiple new targets (for libraries which
might be separated from libjvm, so reduce the size and startup time of
the VM.

In order to support multiple targets being built (agent, libjsig,
etc., in addition to libjvm) the makefiles should be rewritten to
support independently buildable targets.