message: Guard code in fmsconvert.cpp with MFEM_USE_FMS so it will compile using the Makefile-based build system.
diff: // MFEM is free software; you can redistribute it and/or modify it under the
  // terms of the BSD-3 license. We welcome feedback and contributions, see file
  // CONTRIBUTING.md for details.
  +#include "../config/config.hpp"
  +
  +#ifdef MFEM_USE_FMS
  #include "fmsconvert.hpp"
  -#include <unordered_map>
  #include <climits>
  using std::endl;
  @@ -1862,3 +1864,4 @@ DataCollectionToFmsDataCollection(DataCollection *mfem_dc,
  }
  } // end namespace mfem
  +#endif
  