Internalized string "break" kept by the parser

The parser uses "break" as fake label to compile "break" as "goto
break". To avoid producing this string at each use, it keeps it
available in its state.

llex.c

@@ -190,6 +190,9 @@ void luaX_setinput (lua_State *L, LexState *ls, ZIO *z, TString *source,
   ls->lastline = 1;
   ls->source = source;
   ls->envn = luaS_newliteral(L, LUA_ENV);  /* get env name */
+  ls->brkn = luaS_newliteral(L, "break");  /* get "break" name */
+  /* "break" cannot be collected, as it is a reserved word" */
+  lua_assert(isreserved(ls->brkn));
   luaZ_resizebuffer(ls->L, ls->buff, LUA_MINBUFFER);  /* initialize buffer */
 }