[IR] Tweaks to receiveArg method in IR interpreter

* Moved code for uncommon arg-receive instructions to receiveArg
  virtual method and set-result in each case stmt. Reduces code
  size in interpreter + additional specialization sites for JVM.

* Additional ~3% speedup in total runtime (365 -> 355 sec).
  Overall, 35% slower than -X-C
  Red-black-tree within 10% of -X-C