Building python for aarch64 / ppc64le

I'm interested in fixing up these build rules for the third party dependencies so that they will build on arm64 and powerpc.
Primarily this is failing in the openssl and python builds at the moment. I can use the bazelify.sh script to generate a valid build file for openssl but what is the best approach for creating a build file that will work across all 3 platforms?
I suspect changing the generation to generate .bzl files which contain functions that return a select for the appropriate platform would be the approach here? This way the bazelify.sh script would be used on each platform to generate the appropriate files rather then trying to have a single build file that supports all 3 platforms?