Code like the following does not compile:

version(Windows)
{
    import core.sys.windows.dll : SimpleDllMain;
    mixin SimpleDllMain;
}

Because SimpleDllMain depends on dll_process_attach, dll_process_detach, dll_thread_attach and dll_thread_detach from core.sys.windows.dll. Statically importing the module, or using a renamed import, would also break the mixin.

It would probably be a robust fix to add:

import core.sys.windows.dll : dll_process_attach, dll_process_detach, dll_thread_attach, dll_thread_detach;

To the body of the DllMain function inside the mixin.