There's been a new version of the portable PolarSSL library released very recently.
It now supports deterministic ECDSA (RFC 6979) secp256k1 and RIPEMD160 and has it's own big number implementation.
From my limited knowledge it looks to me like it contains all of the functionality required to perform the cryptographic parts of Bitcoin hashing and signing.
I've only looked over the webpage but it appears that this new version could be used instead of OpenSSL for hashing, key / address generation and ECDSA signing.
With the new Bitcoin related features added in the recent release it looks promising.
Has anyone used this yet ?
https://polarssl.org/tech-updates/releases/polarssl-1.3.4-released