It turns out the issues I was having compiling OATH-Toolkit was due to a slight change to the build process introduced in version 1.8.1. It is something to do with autoreconf, but I wasn't able to properly diagnose the problem. Ergo my workaround was to simply build only the parts that I needed:
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wget http://download.savannah.gnu.org/releases/oath-toolkit/oath-toolkit-1.10.2.tar.gz tar -xzf oath-toolkit-1.10.2.tar.gz cd oath-toolkit-1.10.2 ./configure make -C liboath make -C pam_oath make -C liboath install make -C pam_oath install
And now I have time-based one-time-passwords on my Mac as well. The next thing to do is figure out how to get it to check against hashed passwords so I can get back to using a single prompt...