[TEST] Add unit tests for libc

[BWindey]

This PR aims to add unit tests for libc.

Along the way, I also discovered some issues with the bindings currently present. Some pointers being misaligned (void * instead of void*), but also a wrong return type for libc::bsearch().

This is a draft PR, because I'm far from done, but would like some input on how thorough these tests should be. I feel like they shouldn't be that thorough, because they should be battle-tested C-code, we're just testing that we can call them from C3, and potentially providing an example for people.

[lerno]

Is this still a draft?

[BWindey]

Yes, I'm not ready yet with most functions.
I don't think I can write tests for every binding in libc, but I can at least check if they are right (correct types), and for the simple ones write a simple test to see if all works as expected.

I'm a bit busy at the moment, but would like to get this out of draft status within at most 2 weeks, preferably 1 week.

[BWindey]

Update: I've been working on this when I have time, and the original timeline is a bit unrealistic. For most functions I have to check if they are correct and if they are ISO C or just POSIX (and thus need @if(!env::WIN32)). The worst ones are where the specification does not the layout of a type, and need to be implemented differently on different platforms.
It's an interesting learning experience for me, but it means that this will take a bit longer then expected.