Static-ify rsaenh/mpi?

[Francois Gouget]

So dlls/rsaenh/mpi.c defines 13 functions that are only used there. So 
they could be made static by tweaking mpi.c and tomcrypt.h.

However my understanding is that this files has been imported in Wine 
from another project so maybe it's not a good idea to diverge much from 
them.

What do you think?
Should we just leave them as is?