You can use QT with CodeBlocks or wxWidgets with QT Creator aswell if you want (and neither QT nor wxWidgets are really suitable for game GUIs anyway), both IDEs use the same compiler (gcc) and thus are compatible with exactly the same libraries so it really is all about your personal preferences. (Personally i prefer QT Creator because of FakeVim), Both are C++ IDEs and have very little support for other languages, (You can integrate Lua or JavaScript in your C++ applications but the IDEs don't have things like syntax highlighting or codecompletion for Lua or JavaScript code.
(There might be plugins for it though).

If you want a multi language IDE i'd recommend looking at NetBeans (its really a Java IDE but it has plugins for pretty much any language you can think of and works reasonably well C++ and JavaScript (not sure about Lua as i usually just use vim to edit scripts)

I was using CodeBlocks for a very short while. It's bearable but I don't recommend, the editor is not very nice... Right now I'm using VC++ Express (free edition), it's more convenient for actual coding (generally, VC++ is the only piece of software by Microsoft that is actually better than all other alternatives, I had situations where my system was so unstable that even notepad was crashing, still VC never crashed for me ever ). But CodeBlocks is very nice in terms of code portability... Ideally, I would go for doing primary coding in VC++ and then move to CodeBlocks for final muliplatform deplyment (note I have not done this yet, there might be some pitfals I'm not aware of).

The IDE you'll use should really not be much of a consideration as far as cross-platform-ness of your game is concerned. You'll do the bulk of your development on one platform or another, and you should use the best, most-productive means of developing software that it has available for your needs.

There's some additional overhead in maintaining multiple IDE project or make files, but most middleware libraries or engines that give you the source code manage this just fine. Tools like CMake can generate these kinds of files in many flavors from a single source document.

For myself, I'd do the bulk of development on Windows using Visual Studio (which is hands-down the best IDE, though some swear by SlickEdit) and manage the project files using CMake. For coding on other platforms (for example, when writing code specific to that platform) I'd likely use VIM, Make, and GDB.

Keep in mind that probably less than 20% of your code will be "platform aware", so you can do probably 80-90% of all your development in one environment. You can even do all your coding in one environment if you set up a cross-compiler, with appropriate libraries, and have a system to deploy builds to the target platform's test machine.