CxxUtils, etc: Add header to suppress a boost deprecated header warning.

In boost 1.87, the boost header detail/atomic_count.hpp is deprecated. However, the spirit parser still includes it. This ends up giving deprecation warnings in dev4LCG for everything that includes the Gaudi parsing headers.

Add a header here to allow suppressing those warnings. For how, do that only for the one specific version 1.87. This has to be done before any other boost headers are included, so we can't really put it in the Gaudi parser headers.