Windows target (mingw) with forceGtk build fails to find GTK entry point.
While building for a windows target works fine, using `-d:forceGtk` results in an error:
`The procedure entry point at atk_hyperlink_impl_get_type could not be located in the dynamic link library...`

![image](https://user-images.githubusercontent.com/8235002/55031745-41b10e00-4fdd-11e9-9ac4-32143736d52c.png)

I confirmed that the mentioned DLL does exist in the path given in the error message.

