Add C function interface to Okra that can be loaded via dlopen/dlsym

We want to add a C interface to Okra that we can load and use by dlopen/dlsym. The user of this API does not have to be a Java application or use JNIenv, etc. We will use this API for new work related to the OpenJDK Sumatra project. The example app shows how to pass in a C string of HSAIL code to build and run the kernel using this new API.