In January upstream moved /usr/bin/enchant and the libraries to enchant-2, hence spell checking doesn't work anymore, when building claws against the current release of enchant.
Several distros, not only rolling releases already migrated to the latest release of enchant.
[rocketmouse@archlinux ~]$ claws-mail -v
Claws Mail version 3.16.0git97
[rocketmouse@archlinux ~]$ enchant-2 -v
@(#) International Ispell Version 3.1.20 (but really Enchant 2.2.3)