FindGIF doesn't support recent giflib versions
FindGIF only checks for giflib versions 3 (or earlier) and 4.
giflib version 5 came out around 2012, making some breaking API changes, so it's definitely worth distinguishing between 4 and 5.
The giflib version labelling has always been a bit ad-hoc (which FindGIF deals with), but since v4.1.6 it's been cleaned up: (From http://giflib.sourceforge.net/gif_lib.html#compatibility )
Versions up to 4.1.6 defined a GIF_LIB_VERSION macro that was string-valued with a tricky format to parse. This macro has been retired.
Versions after 4.1.6 define integer-valued GIFLIB_MAJOR, GIFLIB_MINOR, and GIFLIB_RELEASE macros for the three components of the version. See the NEWS file in the GIFLIB distribution to track API changes.
So it'd be lovely if FindGIF could be updated to use the new defined if they are available.