[chore] Switch libffi to PARALLEL_JOBS
[chore] Switch libffi to PARALLEL_JOBS

Leftover from 9bad2e83870de728e00ce387136a4e0fa4827de4.

koreader/koreader-base,houqp/koreader-base,Frenzie/koreader-base,houqp/koreader-base,koreader/koreader-base,apletnev/koreader-base,NiLuJe/koreader-base,NiLuJe/koreader-base,koreader/koreader-base,Frenzie/koreader-base,NiLuJe/koreader-base,Frenzie/koreader-base,Frenzie/koreader-base,houqp/koreader-base,apletnev/koreader-base,houqp/koreader-base,NiLuJe/koreader-base,apletnev/koreader-base,apletnev/koreader-base,koreader/koreader-base