The release files uploaded to SourceForge for both giflib-5.1.6 and giflib-5.1.5 both appear to contain broken symlinks in place of the actual files for the Makefile as well as the files in the tests/ directory:
$ tar tzvf gitlib-5.1.6.tar.gz
hrw-rw-r-- 0 esr esr 0 Feb 12 14:26 giflib-5.1.6/Makefile link to giflib-5.1.6/Makefile
drwxrwxr-x 0 esr esr 0 Feb 10 22:36 giflib-5.1.6/tests/
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/treescap.ico link to giflib-5.1.6/tests/treescap.ico
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/x-trans.map link to giflib-5.1.6/tests/x-trans.map
hrw-rw-r-- 0 esr esr 0 Oct 17 2012 giflib-5.1.6/tests/wedge.gif link to giflib-5.1.6/tests/wedge.gif
hrw-rw-r-- 0 esr esr 0 Apr 2 2016 giflib-5.1.6/tests/treescap-interlaced.rgb link to giflib-5.1.6/tests/treescap-interlaced.rgb
hrw-rw-r-- 0 esr esr 0 Apr 2 2016 giflib-5.1.6/tests/gifgrid.ico link to giflib-5.1.6/tests/gifgrid.ico
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/foobar.ico link to giflib-5.1.6/tests/foobar.ico
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/giffixed.ico link to giflib-5.1.6/tests/giffixed.ico
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/porsche.map link to giflib-5.1.6/tests/porsche.map
hrw-rw-r-- 0 esr esr 0 Apr 2 2016 giflib-5.1.6/tests/welcome2.rgb link to giflib-5.1.6/tests/welcome2.rgb
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/solid2.map link to giflib-5.1.6/tests/solid2.map
hrw-rw-r-- 0 esr esr 0 Apr 2 2016 giflib-5.1.6/tests/porsche.rgb link to giflib-5.1.6/tests/porsche.rgb
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/treescap-interlaced.dmp link to giflib-5.1.6/tests/treescap-interlaced.dmp
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/treescap.dmp link to giflib-5.1.6/tests/treescap.dmp
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/solid2.dmp link to giflib-5.1.6/tests/solid2.dmp
hrw-rw-r-- 0 esr esr 0 Apr 2 2016 giflib-5.1.6/tests/solid2.rgb link to giflib-5.1.6/tests/solid2.rgb
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/welcome2.map link to giflib-5.1.6/tests/welcome2.map
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/gifgrid.dmp link to giflib-5.1.6/tests/gifgrid.dmp
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/fire.map link to giflib-5.1.6/tests/fire.map
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/x-trans.dmp link to giflib-5.1.6/tests/x-trans.dmp
hrw-rw-r-- 0 esr esr 0 Apr 2 2016 giflib-5.1.6/tests/x-trans.rgb link to giflib-5.1.6/tests/x-trans.rgb
hrw-rw-r-- 0 esr esr 0 Apr 2 2016 giflib-5.1.6/tests/gifgrid.rgb link to giflib-5.1.6/tests/gifgrid.rgb
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/treescap-interlaced.map link to giflib-5.1.6/tests/treescap-interlaced.map
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/fire.dmp link to giflib-5.1.6/tests/fire.dmp
hrw-rw-r-- 0 esr esr 0 Apr 2 2016 giflib-5.1.6/tests/treescap.rgb link to giflib-5.1.6/tests/treescap.rgb
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/treescap.map link to giflib-5.1.6/tests/treescap.map
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/porsche.dmp link to giflib-5.1.6/tests/porsche.dmp
hrw-rw-r-- 0 esr esr 0 Feb 10 22:36 giflib-5.1.6/tests/makefile link to giflib-5.1.6/tests/makefile
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/gifgrid.map link to giflib-5.1.6/tests/gifgrid.map
hrw-rw-r-- 0 esr esr 0 Apr 2 2016 giflib-5.1.6/tests/fire.rgb link to giflib-5.1.6/tests/fire.rgb
hrw-rw-r-- 0 esr esr 0 May 16 2014 giflib-5.1.6/tests/welcome2.dmp link to giflib-5.1.6/tests/welcome2.dmp
$ tar xzf giflib-5.1.6.tar.gz
giflib-5.1.6/Makefile: Can't create 'giflib-5.1.6/Makefile'
giflib-5.1.6/tests/treescap.ico: Can't create 'giflib-5.1.6/tests/treescap.ico'
giflib-5.1.6/tests/x-trans.map: Can't create 'giflib-5.1.6/tests/x-trans.map'
giflib-5.1.6/tests/wedge.gif: Can't create 'giflib-5.1.6/tests/wedge.gif'
giflib-5.1.6/tests/treescap-interlaced.rgb: Can't create 'giflib-5.1.6/tests/treescap-interlaced.rgb'
giflib-5.1.6/tests/gifgrid.ico: Can't create 'giflib-5.1.6/tests/gifgrid.ico'
giflib-5.1.6/tests/foobar.ico: Can't create 'giflib-5.1.6/tests/foobar.ico'
giflib-5.1.6/tests/giffixed.ico: Can't create 'giflib-5.1.6/tests/giffixed.ico'
giflib-5.1.6/tests/porsche.map: Can't create 'giflib-5.1.6/tests/porsche.map'
giflib-5.1.6/tests/welcome2.rgb: Can't create 'giflib-5.1.6/tests/welcome2.rgb'
giflib-5.1.6/tests/solid2.map: Can't create 'giflib-5.1.6/tests/solid2.map'
giflib-5.1.6/tests/porsche.rgb: Can't create 'giflib-5.1.6/tests/porsche.rgb'
giflib-5.1.6/tests/treescap-interlaced.dmp: Can't create 'giflib-5.1.6/tests/treescap-interlaced.dmp'
giflib-5.1.6/tests/treescap.dmp: Can't create 'giflib-5.1.6/tests/treescap.dmp'
giflib-5.1.6/tests/solid2.dmp: Can't create 'giflib-5.1.6/tests/solid2.dmp'
giflib-5.1.6/tests/solid2.rgb: Can't create 'giflib-5.1.6/tests/solid2.rgb'
giflib-5.1.6/tests/welcome2.map: Can't create 'giflib-5.1.6/tests/welcome2.map'
giflib-5.1.6/tests/gifgrid.dmp: Can't create 'giflib-5.1.6/tests/gifgrid.dmp'
giflib-5.1.6/tests/fire.map: Can't create 'giflib-5.1.6/tests/fire.map'
giflib-5.1.6/tests/x-trans.dmp: Can't create 'giflib-5.1.6/tests/x-trans.dmp'
giflib-5.1.6/tests/x-trans.rgb: Can't create 'giflib-5.1.6/tests/x-trans.rgb'
giflib-5.1.6/tests/gifgrid.rgb: Can't create 'giflib-5.1.6/tests/gifgrid.rgb'
giflib-5.1.6/tests/treescap-interlaced.map: Can't create 'giflib-5.1.6/tests/treescap-interlaced.map'
giflib-5.1.6/tests/fire.dmp: Can't create 'giflib-5.1.6/tests/fire.dmp'
giflib-5.1.6/tests/treescap.rgb: Can't create 'giflib-5.1.6/tests/treescap.rgb'
giflib-5.1.6/tests/treescap.map: Can't create 'giflib-5.1.6/tests/treescap.map'
giflib-5.1.6/tests/porsche.dmp: Can't create 'giflib-5.1.6/tests/porsche.dmp'
giflib-5.1.6/tests/makefile: Can't create 'giflib-5.1.6/tests/makefile'
giflib-5.1.6/tests/gifgrid.map: Can't create 'giflib-5.1.6/tests/gifgrid.map'
giflib-5.1.6/tests/fire.rgb: Can't create 'giflib-5.1.6/tests/fire.rgb'
giflib-5.1.6/tests/welcome2.dmp: Can't create 'giflib-5.1.6/tests/welcome2.dmp'
tar: Error exit delayed from previous errors.
Fixed in head, 5.1.7 will ship shortly.