Issue #16840: Turn on support of bignums only in final release of Tcl 8.5.

diff --cc Modules/_tkinter.c
index 241c1a0a4d872e5cc545d1f7f98f01ce34e20868,491a8fe283a2eca5f23f7a01e1d21570b4327ad2..3f5835363ab635f9eec84e729b8c6a219268f4ac
--- 1/Modules/_tkinter.c
--- 2/Modules/_tkinter.c
+++ b/Modules/_tkinter.c
@@@ -52,11 -58,18 +52,11 @@@ Copyright (C) 1994 Steen Lumholt
  
  #include "tkinter.h"
  
 -/* For Tcl 8.2 and 8.3, CONST* is not defined (except on Cygwin). */
 -#ifndef CONST84_RETURN
 -#define CONST84_RETURN
 -#undef CONST
 -#define CONST
 -#endif
 -
 -#if TK_VERSION_HEX < 0x08030102
 -#error "Tk older than 8.3.1 not supported"
 +#if TK_VERSION_HEX < 0x08040002
 +#error "Tk older than 8.4 not supported"
  #endif
  
- #if TK_VERSION_HEX >= 0x08050000
+ #if TK_VERSION_HEX >= 0x08050002
  #define HAVE_LIBTOMMAMTH
  #include <tclTomMath.h>
  #endif