Build fails on FreeBSD: make: illegal argument to -j -- must be positive integer!

[yonas]

$ cargo build --release -p winterjs
...
error: failed to run custom build command for `mozjs_sys v0.68.2 (https://github.com/wasmerio/mozjs.git?branch=fix-obj-file-lists#f6cbd122)`

Caused by:
  process didn't exit successfully: `/git/winterjs/target/release/build/mozjs_sys-d8b0cf7cba3788c2/build-script-build` (exit status: 101)
  --- stdout
  cargo:outdir=/git/winterjs/target/release/build/mozjs_sys-456e9eb6b048a812/out/build

  --- stderr
  gmake: *** No targets specified and no makefile found.  Stop.
  make: illegal argument to -j -- must be positive integer!
  thread 'main' panicked at /home/yonas/.cargo/git/checkouts/mozjs-e1c76167ba7c548f/f6cbd12/mozjs-sys/build.rs:272:5:
  assertion failed: result.success()
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...

commit: 2996a93