Upstream has released updates that appear to apply and compile correctly.
This update has not been tested by PaperMC and as with ANY update, please do your own testing
Bukkit Changes:
4727d326 Don't let Sign extend SignSide, mark API as experimental
9b29bdcc PR-845: Add preliminary support for multi sided signs
CraftBukkit Changes:
b346a5f6d PR-1170: Add preliminary support for multi sided signs
86c816189 Update SQLite version
d9324b4bc Fix addition of custom smithing trim / transform recipes
Spigot Changes:
7d7b241e Rebuild patches