@dopplershift, a good way to take advantage of the existing recipe work for a package is to add exit 1 to the end of build.sh, then when the build fails, all the artefacts are in place for you and a script is placed in the work directory that you can source and that script will activate the envs and set all the env vars needed to allow you to hack further. A good tip is to use -m conda_build_config-dbg.yaml so that things are built with reasonable debugging flags (pointing at https://github.com/AnacondaRecipes/aggregate/blob/master/conda_build_config-dbg.yaml => I'm about to push a small fix/update for this file though)
@abellgithub for macOS, sysroots are done a bit differently because clang and llvm are messed up in that regard. We added CONDA_BUILD_SYSROOT env. var. This is documented as we've significantly deviated from Apple's way If you are using conda-forge's python and have the compilers installed in your active env. and have CONDA_BUILD_SYSROOT set to point to a good, old macOS SDK then it should work. I'm not running macOS presently though so I cannot check