anchor.diff:  , removeReferencesTo
   , cpp ? false
   , gfortran ? null
  +, fortran2003 ? false
   , zlib ? null
   , szip ? null
   , mpi ? null
  
positive.code: # cpp and mpi options are mutually exclusive
  # (--enable-unsupported could be used to force the build)
  assert !cpp || mpi == null;
  
  # No point splitting version 1.8.18 into multiple outputs.
  # The library /lib/libhdf5.so has a reference to gcc-wrapper
  
negative.code:   configureFlags = []
      ++ optional cpp "--enable-cxx"
      ++ optional (gfortran != null) "--enable-fortran"
      ++ optional fortran2003 "--enable-fortran2003"
      ++ optional (szip != null) "--with-szlib=${szip}"
      ++ optionals (mpi != null) ["--enable-parallel" "CC=${mpi}/bin/mpicc"]
      ++ optional enableShared "--enable-shared";
  