Raw bindings to Apple's Core Audio API for macos and iOS generated using rust-bindgen. coreaudio-rs is an attempt at offering a higher level API around this crate.
Rust Cross has a good explanation of how cross-compiling Rust works in general. While the author of Rust Cross advises against it, it is perfectly possible to cross-compile Rust for MacOS on Linux. OSXCross can be used to create a compiler toolchain that can compile for MacOS on Linux.
When cross-compiling for MacOS on Linux there are two environment variables that are used to configure how coreaudio-sys finds the required headers and libraries. The following examples assume that you have OSXCross installed at /build/osxcross.
This tell coreaudio-sys where to find the MacOS SDK:
export COREAUDIO_SDK_PATH=/build/osxcross/target/SDK/MacOSX10.11.sdk