add option for Mac OSX SDK location in bootstrap.py?

[nextgenusfs]

In order to get OSX recipes to build on my Mac I have to edit the conda_build_config.yaml to add the following:

CONDA_BUILD_SYSROOT:
  - /opt/MacOSX10.9.sdk        # [osx]

Otherwise all builds fail as it isn't pointed to the Mac SDK. I've installed the 10.9sdk in this location as specified https://docs.conda.io/projects/conda-build/en/latest/resources/compiler-tools.html#macos-sdk. Would be nice to either 1) have this be the default in the conda_build_config.yaml or 2) provide a command line option to bootstrap.py to specify the location which would then add the above to the yaml file.

How do others deal with this?

[epruesse]

Exactly like that.

Would you like to add this to our docs?