no more 'luaO_nilobject' to avoid comparison of global variable addresses

(now uses static variables)

lobject.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lobject.c,v 2.124 2018/02/27 18:47:32 roberto Exp roberto $
+** $Id: lobject.c,v 2.125 2018/04/25 16:26:20 roberto Exp roberto $
 ** Some generic functions over Lua objects
 ** See Copyright Notice in lua.h
 */
@@ -29,10 +29,6 @@
 #include "lvm.h"
 
 
-
-LUAI_DDEF const TValue luaO_nilobject_ = {NILCONSTANT};
-
-
 /*
 ** converts an integer to a "floating point byte", represented as
 ** (eeeeexxx), where the real value is (1xxx) * 2^(eeeee - 1) if