add freesasa build flag

[pstjohn]

Edits for #20

Checklist

• [ x ] Used a personal fork of the feedstock to propose changes
• [ x ] Bumped the build number (if the version is unchanged)
• [ ] Reset the build number to 0 (if the version changed)
• [ ] Re-rendered with the latest conda-smithy (Use the phrase code>@<space/conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• [ ] Ensured the license file is being packaged.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[pstjohn]

Looks like it works, but we're running into CI build time limits. Not sure why, would FreeSASA add ~2 hours to the build time? I suppose we split it off into a separate conda recipe and add it as a dependency? https://github.com/intbio/freesasa-conda/tree/master/freesasa

[jaimergp]

ppc64le builds are emulated so they run like 6x slower. We could think of cross-compiling those, but anyway rdkit is vendoring a few dependencies according to the logs, so we should probably provide those as separate packages to depend on, as recommended.

These packages would need to be provided separately:

• catch (https://github.com/catchorg/Catch2/archive/v2.12.4.tar.gz)
• InChI (https://www.inchi-trust.org/download/105/INCHI-1-SRC.zip)
• avalontoolkit (https://sourceforge.net/projects/avalontoolkit/files/AvalonToolkit_1.2/AvalonToolkit_1.2.0.source.tar)
• freesasa (https://github.com/mittinatten/freesasa/releases/download/2.0.3/freesasa-2.0.3.tar.gz)
• maeparser (https://github.com/schrodinger/maeparser/archive/v1.2.4.tar.gz)
• coordgen (https://github.com/schrodinger/coordgenlibs/archive/v2.0.3.tar.gz)
• RingDecomposerLib (https://github.com/rareylab/RingDecomposerLib/archive/v1.1.3_rdkit.tar.gz)

Also, rapidjson (https://github.com/Tencent/rapidjson/archive/v1.1.0.tar.gz) is being vendored but there's a package on CF already. We should use that. I'd recommend closing this and fixing the above issues before. Once these dependencies are provided, new RDKit builds need to be generated.

[mcs07]

Superceded by #80