If your app depends on OpenSSL,you should compile OpenSSL yourself and statically link a known version of OpenSSL into your app. This use of OpenSSL is possible on both OS X and iOS. However, unless you are trying to maintain source compatibility with an existing open source project, you should generally use a different API.
Common Crypto and Security Transforms are the recommended alternatives for general encryption. CFNetwork and Secure Transport are the recommended alternatives for secure communications.