[wxhaskell-devel] Fix for Windows build

[<mac...@gm...>]

Attached is my attempt to fix the Windows build. It should not have
any impact on the builds on other platforms.

The patch contains:
- Dave's fix to conflicting wxEVT definitions
- Eric's wx-config replacement
- my changes to WxConfig and wxcore Setup.hs

Any chance this can be applied to the official repo?

Regards,
Maciek