https://github.com/flightaware/tclx/pull/16#issuecomment-1565348180
--- a/configure.in	2023-03-15 22:00:11.725506240 +0100
+++ b/configure.in	2023-03-15 22:00:29.230246904 +0100
@@ -253,6 +253,7 @@
     
     AC_CHECK_FUNC(inet_aton, , [AC_DEFINE(NO_INET_ATON)])
     AC_CHECK_FUNC(gethostname, , [AC_DEFINE(NO_GETHOSTNAME)])
+    AC_CHECK_FUNCS([rresvport])
     
     #-------------------------------------------------------------------------
     # Check for additional libraries the Tcl/Tk does not check for.
--- a/unix/tclXunixSock.c	2023-03-15 22:02:32.255424538 +0100
+++ b/unix/tclXunixSock.c	2023-03-15 22:03:35.094493443 +0100
@@ -194,10 +194,12 @@
      * Allocate a reserved port if requested.
      */
     if (getReserved) {
+#ifdef HAVE_RRESVPORT
         int port;
         if (rresvport (&port) < 0)
             goto unixError;
         local.sin_port = port;
+#endif
     }
 
     /*