Verify how to represent arrays in function signatures

[tgross35]

E.g. socketpair is:

int socketpair(int domain, int type, int protocol, int sv[2]);

But we have

pub fn socketpair(domain: c_int, type_: c_int, protocol: c_int, socket_vector: *mut c_int) -> c_int;

*mut [c_int; 2] is ABI-compatible and more user-friendly, so we should consider using it and possibly updating ctest to require this kind of thing.

We may not be able to do this in general because technically in C, you can pass more than 2 items. But for most cases this shouldn't be a problem.

[tgross35]

See also my comment at mozilla/cbindgen#171 (comment) where I dug into things a bit

[tgross35]

Also int pipe(int pipefd[2]);