Integrate with Litmus PGM support.

Make use of liblitmus's interface for signalling
a task's waiting for tokens.
Optimize compiled code for the native platform.
pgmrt: Do busy work to simulate real work

Updated pgmrt to actually perform computations for the execution time
specified for each node/task/job. Loop method based upon liblitmus's
rtspin.

Note: Loop touches a big array of data. This will have to change when
pgmrt becomes working-set-size aware. That is, we don't want the busy
work to impose a larger working set of memory than the user specifies.