When i do

Export {
        Depends { name: "cpp" }
        cpp.staticLibraries: [
             sourceDirectory +"/lib/somelib.lib",
             "gdi32"
             ]
    }

I got error "cannot find -lD:/dev/ ... lib/somelib.lib" and in liner command line i see that it is passed with -l.

You check is it library for mingw using 'staticLibrarySuffix: ".a" as possible suffix, but gcc can link ".lib" files as well.