[RFC] Adding unit test for rlibc

We are pulling in rlibc into Zinc (hackndev/zinc#113), but while reading the code, I though it could do with some unit tests.

So I have added some tests here, but seem like there are a few issues... Please see comments with `XXX` and respond if you have any thoughts :+1:
This will need to stay rather than being commented out. You can follow the same test strategy of crates like `libcollections` which have lots of `#[cfg(test)]` directives at the top.