libltdl: fix gcc compiler warning for unused attributes.

* libltdl/ltdl.c, libltdl/loaders/dld_link.c,
libltdl/loaders/dlopen.c, libltdl/loaders/dyld.c,
libltdl/loaders/load_add_on.c, libltdl/loaders/loadlibrary.c,
libltdl/loaders/preopen.c, libltdl/loaders/shl_load.c: For at
least gcc 4.8.3 and 4.9.1, __attribute__((__unused)) should
follow the unused parameter declaration.
* NO-THANKS: Add Дилян Палаузов.
Reported by Дилян Палаузов

Signed-off-by: Gary V. Vaughan <gary@gnu.org>