I'm running the Arch User Repository build written by me:
https://aur.archlinux.org/cgit/aur.g...LD?h=sigil-git
(Also I've filed a bugreport on the ArchLinux bugtracker to update the community sigil package with those changes. Quite surprisingly, for Arch anyway, it's been a few days and we still didn't get the update.

)
Never did figure out
why qt5-multimedia was listed as a build dependency?