[Cython] make __pyx_modulename have static storage

[Stefan Behnel]

Lisandro Dalcin wrote:
> Just noticed this line (reported by Intel compiler)
> 
> const char *__pyx_modulename = "mpi4py.MPI";
> 
> Any good reason to not make it have "static" storage?

No, it shouldn't be used anywhere else anyway.

Stefan