x64: Allow building with LUAJIT_USE_SYSMALLOC and LUAJIT_USE_VALGRIND.

Valgrind 3.9 killed MAP_32BIT support. Ugh. So now we have to rely on
undocumented behavior where Valgrind always allocates from the bottom
of memory. Alas, such a binary won't run properly without Valgrind.

src/lj_state.c

@@ -175,7 +175,7 @@ static void close_state(lua_State *L)
     g->allocf(g->allocd, G2GG(g), sizeof(GG_State), 0);
 }
 
-#if LJ_64
+#if LJ_64 && !(defined(LUAJIT_USE_VALGRIND) && defined(LUAJIT_USE_SYSMALLOC))
 lua_State *lj_state_newstate(lua_Alloc f, void *ud)
 #else
 LUA_API lua_State *lua_newstate(lua_Alloc f, void *ud)