I figured out the cause. It looks like a bug in QtCreator or the Qt config process in how it handles the Microsoft LIB environment variable. GCC is choking on this:

-L"c:\Program Files\Microsoft Visual Studio .NET 2003\SDK\v1.1\Lib\"

because it ends in a trailing backslash and that somehow confuses it. Qt copies that Microsoft environment variable to the linker command line without removing the trailing backslash. I tend to think that's a bug.

To fix it you need to modify your environment variable yourself in your Windows settings or you need to somehow fix the QT install. How? Edit a config file somewhere?