Improve full-lightuserdata check on 32-bit platforms.

On 32-bit platforms, full-lightuserdata is always supported since their pointer fits entirely in 2^48 limitation that LuaJIT had in older version.

Also suppress warning about key > 0x20000000000000ULL is always false on enet.cpp when compiling on 32-bit platforms.

src/common/runtime.cpp

@@ -106,6 +106,10 @@ static bool luax_isfulllightuserdatasupported(lua_State *L)
 	static bool checked = false;
 	static bool supported = false;
 
+	if (sizeof(void*) == 4)
+		// 32-bit platforms always supports full-lightuserdata.
+		return true;
+
 	if (!checked)
 	{
 		lua_pushcclosure(L, [](lua_State *L) -> int

src/libraries/enet/enet.cpp

@@ -123,6 +123,10 @@ static bool supports_full_lightuserdata(lua_State *L)
 	static bool checked = false;
 	static bool supported = false;
 
+	if (sizeof(void*) == 4)
+		// 32-bit platforms always supports full-lightuserdata.
+		return true;
+
 	if (!checked)
 	{
 		lua_pushcclosure(L, [](lua_State* L) -> int
@@ -168,13 +172,16 @@ static uintptr_t compute_peer_key(lua_State *L, ENetPeer *peer)
 
 static void push_peer_key(lua_State *L, uintptr_t key)
 {
-	// If full 64-bit lightuserdata is supported, always use that. Otherwise,
-	// if the key is smaller than 2^53 (which is integer precision for double
-	// datatype), then push number. Otherwise, throw error.
+	// If full 64-bit lightuserdata is supported (or it's 32-bit platform),
+	// always use that. Otherwise, if the key is smaller than 2^53 (which is
+	// integer precision for double datatype) on 64-bit platform, then push
+	// number. Otherwise, throw error.
 	if (supports_full_lightuserdata(L))
 		lua_pushlightuserdata(L, (void*) key);
+#if UINTPTR_MAX == 0xffffffffffffffff
 	else if (key > 0x20000000000000ULL) // 2^53
 		luaL_error(L, "Cannot push enet peer to Lua: pointer value %p is too large", key);
+#endif
 	else
 		lua_pushnumber(L, (lua_Number) key);
 }