Return sources by arch

def _select_source_arch(self, source, source64):
        """Return sources by arch
        """
        src = ""
        if self.meta.arch == "x86_64":
            if source64:
                src = source64
            else:
                src = source
            if self.meta.skip_unst in self.answer and source64 in self.unst:
                src = source
        else:
            if source:
                src = source
            if self.meta.skip_unst in self.answer and source in self.unst:
                src = source64
        return src