I agree, definitely C. As John Wells
stated, fast & simple (your requirements). There's another couple of advantages, too:
1. Almost _every_ platform has a cc (C compiler, the joke is this used to be the command you used to call the default on most systems and still works on most *nixes -- dunno on MS).
2. Second relates to point 1: it's easy to port. A compiler for C is simple to write from scratch (by design). So if your platform doesn't have a cc, you (or at least someone knowledgeable enough) can whip one up feasibly and quickly.
As an aside, on a purely pragmatic note, I'll tell you one off-topic-ish-y-kinda-thing: when you lose chunks of your memory, a solid C knowledge is a lifesaver.
Really, I consider C the most important language to learn. Even if you don't master it, it's a great tool and excellent foundation. It's also one of the few you can truly self-study (so long as you know basically how a PC works, you don't need to be an engineer).