CI ARM: Buster armhf compatibility

Allow 32-bit builds on Buster. This has some advantages
regarding supported HW accelerations in UltraGrid, eg. h264_omx is not
supported in higher versions of the system.

It is not enabled by default but can be enabled easily by switching the
value in YAML file.

refers to GH-344

.github/scripts/Linux/arm/bootstrap.sh

@@ -1,6 +1,7 @@
 #!/bin/sh -exu
 
-readonly debver=bullseye
+debver=$(. /etc/os-release; echo "$VERSION_CODENAME")
+readonly debver
 
 apt -y install curl gnupg
 echo -k > ~/.curlrc
@@ -20,7 +21,14 @@ http://archive.raspberrypi.org/debian $debver main
 EOF
 apt -y update
 
-apt -y install autoconf automake build-essential cmake git pkg-config libtool sudo
+if [ "$debver" = buster ]; then
+        # 3.16 in the added repository is broken with chrooted qemu-user-static
+        apt -y install cmake=3.13.4-1 cmake-data=3.13.4-1
+else
+        apt -y install cmake
+fi
+
+apt -y install autoconf automake build-essential git pkg-config libtool sudo
 apt -y install libcurl4-openssl-dev libsoxr-dev libspeexdsp-dev libssl-dev
 apt -y install libasound2-dev portaudio19-dev libjack-dev
 apt -y install libglew-dev libglfw3-dev libglm-dev

.github/workflows/arm-build.yml

@@ -20,10 +20,12 @@ jobs:
             repo: http://mirrordirector.raspbian.org/raspbian/
             keyring: /etc/apt/trusted.gpg
             qemu_bin_arch: arm
+            deb_release: bullseye
           - arch: arm64
             repo: https://deb.debian.org/debian
             keyring: /usr/share/keyrings/debian-archive-keyring.gpg
             qemu_bin_arch: aarch64
+            deb_release: bullseye
 
     steps:
     - uses: actions/checkout@v3
@@ -60,7 +62,7 @@ jobs:
         sudo mkdir -p ~/chroot/var/tmp
         sudo mv /var/tmp/*NDI* ~/chroot/var/tmp
         wget http://archive.raspbian.org/raspbian.public.key -O - | sudo apt-key add -q
-        sudo debootstrap --keyring=${{ matrix.keyring }} --arch ${{ matrix.arch }} bullseye ~/chroot ${{ matrix.repo }}
+        sudo debootstrap --keyring=${{ matrix.keyring }} --arch ${{ matrix.arch }} ${{ matrix.deb_release }} ~/chroot ${{ matrix.repo }}
         sudo cp -r $GITHUB_WORKSPACE/.github ~/chroot
         sudo cp /usr/bin/qemu-${{ matrix.qemu_bin_arch }}-static ~/chroot/usr/bin
         sudo chroot ~/chroot /.github/scripts/Linux/arm/bootstrap.sh ${{ matrix.arch }}