It's not in POSIX and Google finds only nmh code containing it.
Maybe it was some BSD experiment. Who knows.
                } else {
                        linkerr = errno;
 
-#ifdef EISREMOTE
-                       if (linkerr == EISREMOTE)
-                               linkerr = EXDEV;
-#endif /* EISREMOTE */
-
                        /*
                        ** Check if the file in our desired location is
                        ** the same as the source file.  If so, then just
 
                vec[vecp++] = "-dist";
                distfile = getcpy(m_mktemp2(altmsg, invo_name, NULL, NULL));
                if (link(altmsg, distfile) == NOTOK) {
-                       if (errno != EXDEV
-#ifdef EISREMOTE
-                                       && errno != EISREMOTE
-#endif /* EISREMOTE */
-                               )
+                       if (errno != EXDEV)
                                adios(distfile, "unable to link %s to",
                                                altmsg);
                        free(distfile);