Force static value for LUAL_BUFFERSIZE

In Lua 5.3.3, LUAL_BUFFERSIZE always equaled the constant since LUA_FLOAT_LONGDOUBLE was always defined.
This check changed in 5.3.4 and the alternate path was being used for LUAL_BUFFERSIZE and triggering
old-style cast warnings in Scons + GCC. Hopefully this gets fixed for 5.3.5.

The following patch constitutes the changes (though they were applied by hand):

*** luaconf.h.old       2017-10-09 23:38:22.641645801 -0500
--- luaconf.h   2017-10-09 23:38:56.548577911 -0500
***************
*** 748,758 ****
  ** smaller buffer would force a memory allocation for each call to
  ** 'string.format'.)
  */
- #if LUA_FLOAT_TYPE == LUA_FLOAT_LONGDOUBLE
  #define LUAL_BUFFERSIZE               8192
- #else
- #define LUAL_BUFFERSIZE   ((int)(0x80 * sizeof(void*) * sizeof(lua_Integer)))
- #endif

  /* }================================================================== */

--- 748,754 ----

src/lua/luaconf.h

@@ -748,11 +748,7 @@
 ** smaller buffer would force a memory allocation for each call to
 ** 'string.format'.)
 */
-#if LUA_FLOAT_TYPE == LUA_FLOAT_LONGDOUBLE
 #define LUAL_BUFFERSIZE		8192
-#else
-#define LUAL_BUFFERSIZE   ((int)(0x80 * sizeof(void*) * sizeof(lua_Integer)))
-#endif
 
 /* }================================================================== */