P.S.: As a workaround, compiling and manually installing https://www.enigmail.net/download/source/enigmail-1.9.7.tar.gz seems to work (Enigmail is active again). Personally, I did not encounter any problem with the Debian version of enigmail preceding this update, so I suggest keeping it to that version for powerpc, if there are no other security implications (did not have the time to sort them out, but basically messages sent encrypted were sent encrypted, never in clear).
-- Stiepan A. Kovac M Sc ICT Security IT+Tech. Tel. Eng.