Build 32 bit Android against API level 23

Which is Android 6, rather than against newer versions. This is also how
we do it on F-Droid, since that gives broader compatibility. Older
Android versions stop working when we target a too high SDK, but
targeting the most recent SDK is pretty much required due to Google
blocking stuff built against older ones claiming that the application is
insecure, even if we don't use anything security-relevant in it.

.github/workflows/main.yml

@@ -106,23 +106,23 @@ jobs:
             cross_qt_args: >-
               "-DANDROID_SDK_ROOT=$ANDROID_SDK_ROOT"
               "-DANDROID_NDK_ROOT=$ANDROID_NDK_ROOT"
-              "-DANDROID_PLATFORM=$ANDROID_PLATFORM"
+              "-DANDROID_PLATFORM=$ANDROID_TARGET_PLATFORM"
               -DANDROID_ABI=arm64-v8a
             cross_ffmpeg_args: >-
               "-DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_TOOLCHAIN_FILE"
               "-DANDROID_SDK_ROOT=$ANDROID_SDK_ROOT"
               "-DANDROID_NDK_ROOT=$ANDROID_NDK_ROOT"
-              "-DANDROID_PLATFORM=$ANDROID_PLATFORM"
+              "-DANDROID_PLATFORM=$ANDROID_TARGET_PLATFORM"
               -DANDROID_ABI=arm64-v8a
             cross_other_args: >-
               "-DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_TOOLCHAIN_FILE"
               "-DANDROID_SDK_ROOT=$ANDROID_SDK_ROOT"
               "-DANDROID_NDK_ROOT=$ANDROID_NDK_ROOT"
-              "-DANDROID_PLATFORM=$ANDROID_PLATFORM"
+              "-DANDROID_PLATFORM=$ANDROID_TARGET_PLATFORM"
               -DANDROID_ABI=arm64-v8a
             build_flags: >-
               "-DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_TOOLCHAIN_FILE"
-              "-DANDROID_PLATFORM=$ANDROID_PLATFORM"
+              "-DANDROID_PLATFORM=$ANDROID_TARGET_PLATFORM"
               "-DANDROID_TARGET_SDK_VERSION=$ANDROID_TARGET_SDK_VERSION"
               "-DANDROID_MIN_SDK_VERSION=$ANDROID_MIN_SDK_VERSION"
               "-DANDROID_SDK_BUILD_TOOLS_REVISION=$ANDROID_BUILD_TOOLS_VERSION"
@@ -173,23 +173,23 @@ jobs:
             cross_qt_args: >-
               "-DANDROID_SDK_ROOT=$ANDROID_SDK_ROOT"
               "-DANDROID_NDK_ROOT=$ANDROID_NDK_ROOT"
-              "-DANDROID_PLATFORM=$ANDROID_PLATFORM"
+              "-DANDROID_PLATFORM=$ANDROID_TARGET_PLATFORM"
               -DANDROID_ABI=armeabi-v7a
             cross_ffmpeg_args: >-
               "-DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_TOOLCHAIN_FILE"
               "-DANDROID_SDK_ROOT=$ANDROID_SDK_ROOT"
               "-DANDROID_NDK_ROOT=$ANDROID_NDK_ROOT"
-              "-DANDROID_PLATFORM=$ANDROID_PLATFORM"
+              "-DANDROID_PLATFORM=$ANDROID_TARGET_PLATFORM"
               -DANDROID_ABI=armeabi-v7a
             cross_other_args: >-
               "-DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_TOOLCHAIN_FILE"
               "-DANDROID_SDK_ROOT=$ANDROID_SDK_ROOT"
               "-DANDROID_NDK_ROOT=$ANDROID_NDK_ROOT"
-              "-DANDROID_PLATFORM=$ANDROID_PLATFORM"
+              "-DANDROID_PLATFORM=$ANDROID_TARGET_PLATFORM"
               -DANDROID_ABI=armeabi-v7a
             build_flags: >-
               "-DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_TOOLCHAIN_FILE"
-              "-DANDROID_PLATFORM=$ANDROID_PLATFORM"
+              "-DANDROID_PLATFORM=$ANDROID_TARGET_PLATFORM"
               "-DANDROID_TARGET_SDK_VERSION=$ANDROID_TARGET_SDK_VERSION"
               "-DANDROID_MIN_SDK_VERSION=$ANDROID_MIN_SDK_VERSION"
               "-DANDROID_SDK_BUILD_TOOLS_REVISION=$ANDROID_BUILD_TOOLS_VERSION"
@@ -372,21 +372,33 @@ jobs:
 
       - name: Set Android environment variables
         run: |
+          # Target Android 6+ on 32 bit, Android 11+ on 64 bit. This is
+          # necessary due to mutual incompatibilities, due to older Android
+          # versions not supporting newer features on one hand and Google being
+          # obstructive against older target SDKs on newer Android on the other.
+          if [ "$ANDROID_ARCH" = 'arm32' ]; then
+            target_sdk_version=23
+            min_sdk_version=23
+          else
+            target_sdk_version=34
+            min_sdk_version=30
+          fi
           build_tools_version=34.0.0-rc3
           ndk_version=27.0.12077973
-          target_sdk_version=34
-          min_sdk_version=30
           ndk_root="$ANDROID_SDK_ROOT/ndk/$ndk_version"
           ndk_toolchain_file="$ndk_root/build/cmake/android.toolchain.cmake"
-          platform="android-$target_sdk_version"
+          platform=android-34
           echo "ANDROID_BUILD_TOOLS_VERSION=$build_tools_version" >> "$GITHUB_ENV"
           echo "ANDROID_NDK_VERSION=$ndk_version" >> "$GITHUB_ENV"
           echo "ANDROID_NDK_ROOT=$ndk_root" >> "$GITHUB_ENV"
           echo "ANDROID_NDK_TOOLCHAIN_FILE=$ndk_toolchain_file" >> "$GITHUB_ENV"
           echo "ANDROID_PLATFORM=$platform" >> "$GITHUB_ENV"
+          echo "ANDROID_TARGET_PLATFORM=android-$target_sdk_version" >> "$GITHUB_ENV"
           echo "ANDROID_TARGET_SDK_VERSION=$target_sdk_version" >> "$GITHUB_ENV"
           echo "ANDROID_MIN_SDK_VERSION=$min_sdk_version" >> "$GITHUB_ENV"
         if: matrix.cross_os == 'Android'
+        env:
+          ANDROID_ARCH: '${{ matrix.arch }}'
 
       # Qt's build toolage really likes to auto-detect Android package
       # versions, despite all attempts to specify them explicitly. So we