Build fails on OpenBSD

Howdy! I'm trying to build this project on OpenBSD but I'm getting an odd error:
```
error: failed to run custom build command for `openssl-sys v0.9.45`

Caused by:
process didn't exit successfully: `/tmp/cargo-install0xvzuk/release/build/openssl-sys-ba87a9adac352fdf/build-script-main` (exit code: 101)
--- stdout
cargo:rustc-cfg=const_fn

--- stderr
thread 'main' panicked at 'don't know how to configure OpenSSL for x86_64-unknown-openbsd', /home/gigavinyl/.cargo/registry/src/github.com-1ecc6299db9ec823/openssl-src-111.6.1+1.1.1d/src/lib.rs:180:18
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

warning: build failed, waiting for other jobs to finish...
error: failed to compile `cargo-web v0.6.26`, intermediate artifacts can be found at `/tmp/cargo-install0xvzuk`

Caused by:
build failed
```