Address the issue of garbage collection on MIPS/Nolimips
The code generated by TC does not free dynamically allocated memory for simplicity purpose. While this is negligible for small tests, it renders the execution of big tests (e.g., the Bistromatig or
mini-morpho.tig) more or less intractable.
The issue has been solved for the IA-32 back end in r2893 (see #74) using the Boehm-Demers-Weiser conservative garbage collector (http://www.hpl.hp.com/personal/Hans_Boehm/gc/). The cost of adjusting the generated code to its interface was really small.
We should study how the Boehm-Demers-Weiser GC could be used within Nolimips to solve the MIPS back end issue as well.