enhance PSI patch to resolve more errors w.r.t. memcpy not being in scope

Without this, I was (sometimes?) running into problems like:

{{{
/tmp/easybuild_build/PSI/4.0b4/ictce-4.1.13/psi4.0b4/src/lib/libparallel/mpi_wrapper.h(80): error: the global scope has no "memcpy"
          ::memcpy(static_cast<void*>(data), static_cast<void*>(receive_buffer), sizeof(double)*nelem);
            ^

/tmp/easybuild_build/PSI/4.0b4/ictce-4.1.13/psi4.0b4/src/lib/libparallel/mpi_wrapper.h(104): error: the global scope has no "memcpy"
      SUMMEMBER(double, MPI_DOUBLE)
      ^

/tmp/easybuild_build/PSI/4.0b4/ictce-4.1.13/psi4.0b4/src/lib/libparallel/mpi_wrapper.h(105): error: the global scope has no "memcpy"
      SUMMEMBER(unsigned int, MPI_INT)
}}}