Commit fd9541ad authored by Committed by Federico Mena Quintero
Support cross-compiling with Rust
The primary change here is to add the --target=$(host) option to the cargo build command, so the Rust components are compiled for the target host system specified by the configure command. The cargo target subdirectory also needed to be prefixed with the host triplet for cross-compiling. Some of the crates' build scripts require cross-pkg-config settings in the environment, so they are set for the cargo build command. It's worth noting that Rust targets are limited to built-in values by default, so the --host value given to configure may not be supported. Built in targets can be found by listing the directory src/librustc_back/target in the rustc source. When building with an unsupported target, the user will have to write a target JSON definition file and set the environment variable RUST_TARGET_PATH to its directory (as with building any Rust project). This also sneaks in prefixing the Rust library recipe line with a "+" character to pass the GNU Make jobserver environment and file descriptors, which cargo supports to act as a jobserver client.
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