Build fails on FreeBSD

[wyc]

I suspect it has to do with a BSD-specific issue with the jni crate.

Please see the following build log for system information and reproduction:

$ git clone [email protected]:spruceid/ssi.git
$ git clone [email protected]:spruceid/didkit.git
$ cd didkit/
$ uname -vp
FreeBSD 12.2-RELEASE r366954 GENERIC  amd64
$ cargo build
   Compiling jni v0.17.0
error[E0425]: cannot find value `EXPECTED_JVM_FILENAME` in this scope
  --> /home/wayne/.cargo/registry/src/github.com-1ecc6299db9ec823/jni-0.17.0/build.rs:97:25
   |
97 |         if file_name == EXPECTED_JVM_FILENAME {
   |                         ^^^^^^^^^^^^^^^^^^^^^ not found in this scope

error: aborting due to previous error

For more information about this error, try `rustc --explain E0425`.
error: could not compile `jni`

To learn more, run the command again with --verbose.