Since version 2.3, OpenVPN can be built using PolarSSL as it's crypto backend, instead of OpenSSL. See https://polarssl.org/ for more information on PolarSSL.
Limitations compared to OpenSSL
Note that the PolarSSL variant of OpenVPN does not support the same featureset as the OpenSSL variant. The most prominent differences are listed in the latest README.polarssl.
Building the PolarSSL-enabled OpenVPN
To build using polarssl:
./configure --with-crypto-library=polarssl make make install