To fix it, I did the following:
cd /usr/local/src curl -O http://www.openssl.org/source/openssl-1.0.0.tar.gz tar -xzvf openssl-1.0.0.tar.gz cd openssl-1.0.0.tar.gz ./configure --prefix=/usr/local make sudo make install cd your/path/to/node/src ./configure --prefix=/usr/local make sudo make install make test
(This assumes you're using /usr/local for sources you build, as some recommend.)
Interestingly, and frustratingly, ./configure for Node still reported that openssl was missing. But make test reported no failures, and the createHmac (and other missing functions) were now in the crypto module's exports. Yay!
I post this not only so I have it for reference next time (as I re-image my MBP often), but in case someone else encounters this problem.