RFE: Implement 128-bit packed PTS support

[gary-funck]

To simplify the configuration of GUPC and to improve maintainability, we have been prototyping 128-bit packed PTS support. We verified that this is feasible and were able to pass all GUPC+UPCR harness tests with suitable modifications to the UPCR runtime. We're hopeful that with 128-bit packed PTS's in place that we can deprecate and remove 'struct PTS' support. However, to complete our testing/validation, we need to have 128-bit packed PTS support implemented in upc2c so that we can ensure that all the necessary UPCR changes are in place.