I have good news:

I found out that the @x suffixes aren't needed in the .obj files. I removed the suffixes from the symbols that are unresolved, imported the needed dlls and linked succesfully an exe that worked as normal.

I have written a tool that removes ALL @s. It is not finsihed but it works although it don't remove the numbers after the @. And the standard symbols (MessageBox, WinMain) will lose their @s, too. But these are needed.

Perhaps somebody knows how to fix this???

Best regards
Chris