I recently pushed 'one-shot' build scripts for building GDC.These might help you getting a working GDC compiler targetting windows.
The usage is rather simple:
$ git clone https://github.com/Ace17/toolchains $ toolchains/deploy_toolchain_i686-ace-mingw32 The output is a standalone toolchain targetting MS Windows in: /tmp/toolchains/i686-ace-mingw32. Hope this helps!