Both SNES and Genesis had a devkit made by a company called Psy-Q (they later made dev kits for the saturn and playstation). In addition to that, the company that designed and manufactured the SNES' cpu had released a C compiler for the system, so the tool would have been availible.
There is also TuME ( http://members.aol.com/opentume/ ) which was used by virgin in the early 90's (remember the similarity between aladin and the lion king for both snes and genesis?).