Auto merge of #1467 - gnzlbg:fix_freebsd, r=gnzlbg

Fix FreeBSD

#1440 broke FreeBSD by changing `libc` FreeBSD targets to require a `cfg(freebsdXX)` to be defined, but not updating `build.rs` to define `freebsd11` when `LIBC_CI` is not available. Since `LIBC_CI` is always defined on CI, this issue went undetected.

This PR fixes that issue in the `build.rs` and introduces a build task that tests FreeBSD without `LIBC_CI` on FreeBSD11, although I'm  not sure this would have caught the issue in #1466 .

Closes #1466 .