-saux filename

   Specifies a pathname for the server auxiliary file. When you give a
   filename, do not give a file extension; the idl compiler appends .c
   to the C source file and .o to the object file.  If you do not use
   the -caux argument, the idl compiler appends _saux.c to the C
   source file and _saux.o to the object file. If the -lang cxx option
   is used, the source file will have the .cxx extension.