cmake::OPALConfig: simplify linking against OPAL
In order to facilitate linking against libOPAL, we provide a CMake find file with all the dependencies (libs and headers)
TODO:
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IPPL lib, should be set from a CMake variable
Note: ${IPPL_LIBRARY_DIR}/lib${IPPL_LIBRARY}.a
seems to me a bit like a hack.. feel free to change if you know a better solution.