Refactor way the-eof-object is defined

* libguile/ports.c (scm_init_ice_9_ports): Define the-eof-object here.
  Update a comment.
* module/ice-9/ports.scm: Use the-eof-object definition from C.

libguile/ports.c

@@ -3145,13 +3145,13 @@ scm_init_ice_9_ports (void)
 {
 #include "libguile/ports.x"
 
+  scm_c_define ("the-eof-object", SCM_EOF_VAL);
+
   /* lseek() symbols.  */
   scm_c_define ("SEEK_SET", scm_from_int (SEEK_SET));
   scm_c_define ("SEEK_CUR", scm_from_int (SEEK_CUR));
   scm_c_define ("SEEK_END", scm_from_int (SEEK_END));
 
-  /* These bindings are used when boot-9 turns `current-input-port' et
-     al into parameters.  They are then removed from the guile module.  */
   scm_c_define ("%current-input-port-fluid", cur_inport_fluid);
   scm_c_define ("%current-output-port-fluid", cur_outport_fluid);
   scm_c_define ("%current-error-port-fluid", cur_errport_fluid);

module/ice-9/ports.scm

@@ -461,8 +461,6 @@ written into the port is returned."
   (call-with-output-string
    (lambda (p) (with-error-to-port p thunk))))
 
-(define the-eof-object (call-with-input-string "" (lambda (p) (read-char p))))
-
 (define (inherit-print-state old-port new-port)
   (if (get-print-state old-port)
       (port-with-print-state new-port (get-print-state old-port))