Log Message:
libusb-compat: Add DIST_SUBDIR to avoid checksum error

pkgsrc changes:
---------------
  * Use release archive from Github to avoid the dependency on autotools
    and to remove conflict with the tag archive potentially present in
    ${DISTDIR} which has the same name but a different checksum.
  * Reorder variables to be compliant with pkgsrc policy described in
    doc/Makefile-example.