Protect against RMFEXPORT being defined already
Protect against RMFEXPORT being defined already

We define RMFEXPORT when building SWIG wrappers,
and SWIG 4.1 now reports a fatal error when it is
redefined, so be sure to undefine it first.

salilab/rmf,salilab/rmf,salilab/rmf,salilab/rmf