Problem PMEMD with MPI

A friend of mine asked me about how come his PMEMD compiled with MPI doesnot contain suffix of .mpi that kind of thing. Actually if anyone check the Makefile of PMEMD, he/she will know that there is no such default filename suffix.

pmemd: $(NETCDF_MOD) $(OBJS)
        $(LOAD) $(LOADFLAGS) -o $@ $(OBJS) $(FFT_LIBS) \
        $(NETCDF_LIBS) $(MATH_LIBS) $(MPI_LIBS) $(LOADLIBS)

Where $@ means the name of this makefile rule, which is "pmemd".