Fails to build on FreeBSD

[asomers]

rustc-test fails to build on FreeBSD. The error is:

error[E0425]: cannot find value `HW_AVAILCPU` in module `libc`
    --> /usr/home/somers/.cargo/registry/src/github.aaakk.us.kg-1ecc6299db9ec823/rustc-test-0.3.0/src/lib.rs:1007:44
     |
1007 |         let mut mib = [libc::CTL_HW, libc::HW_AVAILCPU, 0, 0];
     |                                            ^^^^^^^^^^^ not found in `libc`

I think you probably should be using libc::HW_NCPU instead.