OpenCL host library

The API implementations of The OpenCL Runtime and the The OpenCL Platform Layer are compiled to a single dynamic library (e.g., libpocl.so). This library contains all implementations and, if pocl is compiled in the ICD mode, is what the ICD loader accesses. In case pocl is instructed (via -DENABLE_ICD=0) to compile a “directly linkable library”, libOpenCL.so is produced which can be linked directly to the OpenCL programs (instead of linking against the ICD loader).