How to build a cross-compiler with rustc_codegen_gcc

Building libgccjit

With crosstool-ng: follow the instructions on this repo.
Other: Build a GCC cross-compiler like usual, but add --enable-languages=jit, --enable-host-shared, and --disable-multilib to the ./configure arguments for pass 1.

Make sure you set the path to the cross-compiling libgccjit in rustc_codegen_gcc's config.toml.
Make sure you have the linker for your target (for instance m68k-unknown-linux-gnu-gcc) in your $PATH. Currently, the linker name is hardcoded as being $TARGET-gcc.
Use --cross during the prepare step so that the sysroot is patched for the cross-compiling case:
- ./y.sh prepare --cross

If the target is already supported by rustc, use --target-triple to specify the target when building the sysroot:
- ./y.sh build --sysroot --target-triple m68k-unknown-linux-gnu
Specify the target when building your project:
- ./y.sh cargo build --target m68k-unknown-linux-gnu

If the target is not yet supported by the Rust compiler, create a target specification file. Fake the arch specified in your target specification file by replacing it with one that is supported by the Rust compiler.
To build the sysroot, use --target-triple to specify the real target, and use --target to add the absolute path to your target specification file:
- ./y.sh build --sysroot --target-triple m68k-unknown-linux-gnu --target $(pwd)/m68k-unknown-linux-gnu.json
Specify the target specification file when building your project:
- ./y.sh cargo build --target path/to/m68k-unknown-linux-gnu.json

If you get the error /usr/bin/ld: unrecognised emulation mode: m68kelf, make sure you set gcc-path (in config.toml) to the install directory.