build-init: Use SDK arch for SDK extensions...
build-init: Use SDK arch for SDK extensions...

...instead of the app we're building arch.

(cherry picked from commit 30964d2baccc03873c2bdbd7b74db919d62d576f)

flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak