How to cross-compile conda package with local crosstool-ng compiler?

[hpckurt]

I'm trying to cross-compile some conda packages to an unsupported platform (linux-ppc) and running into an issue with the compilers.

As an example, I'm starting with bzip2: https://github.com/conda-forge/bzip2-feedstock

I've added a conda_build_config.yaml file with the following:

c_compiler:
  - powerpc-espresso-linux-gnu-gcc
target_platform:
  - linux-ppc

However, it always results in the following error:

Encountered problems while solving:
  - nothing provides requested c_linux-ppc
  - nothing provides requested powerpc-espresso-linux-gnu-gcc_linux-ppc

While it's true that c_linux-ppc doesn't exist, powerpc-espresso-linux-gnu-gcc_linux-ppc does exist on the local system:

$ powerpc-espresso-linux-gnu-gcc_linux-ppc --version
powerpc-espresso-linux-gnu-gcc_linux-ppc (crosstool-NG 1.26.0) 13.2.0
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

I assume this error is showing up because it's trying to pull powerpc-espresso-linux-gnu-gcc_linux-ppc from a conda repo. How do I force conda-build to use a local compiler?

Any help is appreciated!