https://bugs.winehq.org/show_bug.cgi?id=49637
--- Comment #12 from Zebediah Figura z.figura12@gmail.com --- Are you sure that the .dll.so are generated by this build, and not left over from an earlier build?
Note also that some DLLs have not been converted to PE, and still yield .dll.so even when compiled with mingw. kernelbase.dll is an example of a DLL that should not end in dll.so with a functional mingw.