Potentially fixed autobuild issue for ARM images

backend/Dockerfile-armhf

@@ -1,5 +1,7 @@
 FROM arm32v7/alpine:3.12
 
+COPY qemu-arm-static /usr/bin
+
 ENV UID=1000 \
   GID=1000 \
   USER=youtube

hooks/post_checkout

@@ -0,0 +1,3 @@
+#!/bin/bash
+# downloads a local copy of qemu on docker-hub build machines
+curl -L https://github.com/balena-io/qemu/releases/download/v3.0.0%2Bresin/qemu-3.0.0+resin-arm.tar.gz | tar zxvf - -C . && mv qemu-3.0.0+resin-arm/qemu-arm-static .

hooks/pre_build

@@ -0,0 +1,4 @@
+#!/bin/bash
+# Register qemu-*-static for all supported processors except the 
+# current one, but also remove all registered binfmt_misc before
+docker run --rm --privileged multiarch/qemu-user-static:register --reset