Support x86 macOS

[leehart]

Re: issue #172

[leehart]

On an Intel macOS, attempting conda env create -f environment-pinned-macos-13.yml -n mgenv_v7.2.0
still results in the PackagesNotFoundError:

Channels:
 - conda-forge
 - bioconda
 - conda-forge/label/broken
Platform: osx-64
Collecting package metadata (repodata.json): done
Solving environment: failed

PackagesNotFoundError: The following packages are not available from current channels:

  - clangxx_osx-64==21.1.3=h7e5c614_25
  - clangxx_impl_osx-64==21.1.3=h2770c5a_25
  - clang_osx-64==21.1.3=h7e5c614_25
  - clang_impl_osx-64==21.1.3=h084dc57_25