Drop patch add_hurd_as_supported_platform.diff, it should not be needed anymore now that we demoted the unsupported platforms error to a warning.

Add patch to demote unsupported platform error to a warning so upstream unsupported platforms like Hurd can build in Debian without additional hacks.

Add patch to re-add Hurd as a supported platform. It was lost when upstream defined the concept of supported platforms but was previously building fine in Debian.