New upstream version 5.2.1

+ Drop 03-spelling_fixes.patch and 40_fixtestsuite.diff.
+ Unfuzz and extend (for libutil addition)
  30_link_utils_dynamically.diff.
+ Do not ship gif standards in txt format with giflib-tools.
+ Update symbol file. Symbols which were only accidentally exported were
  removed. For consumption by giflib-tools a small (static) helper library
  (libutil) still provides the symbols.
+ Pass CC=$(CC) to dh_auto_build