gnu: Add ots.

* gnu/packages/patches/ots-no-include-missing-file.patch: New file.
* gnu/packages/ots.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add ots.scm.
  (dist_patch_DATA): Add ots-no-include-missing-file.patch.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>