Workaround to find private Rec files with new CMake configuration

MooreCache uses a file from Rec that is not installed.

Although that was common practice with the CMT and the old-style CMake configuration, it should not be done and if a file in Rec is supposed to be used by downstream projects it should be installed.

This is a kind of temporary workaround, taking into account that when using the new Gaudi configuration classes we should replace options directories with importable Python modules, implicitly fixing the problem of not installed option files.