Choose the best available macOS arch

.github/workflows/build.yaml

@@ -214,8 +214,13 @@ jobs:
         if-no-files-found: error
     - name: Choose target architectures
       run: |
-        # \todo more logic here
-        echo "CMAKE_OSX_ARCHITECTURES=arm64;x86_64" >> $GITHUB_ENV
+        # Qt Online Installer only provides x86-64 binaries (not arm64) prior to Qt 6.2.0.
+        if [[ '${{ matrix.qt }}' =~ ^(5|6\.[01])\. ]]; then arch=x86_64
+        # GitHub's macos-15 runners only support arm64, and no longer support x86-64.
+        elif [[ '${{ matrix.os }} == 'macos-15' ]]; then arch=arm64
+        # Otherwise, default to universal binaries, where possible.
+        else arch='arm64;x86_64'; fi
+        echo "CMAKE_OSX_ARCHITECTURES=${arch}" >> $GITHUB_ENV
     - name: Build
       id: build
       env:
@@ -230,6 +235,7 @@ jobs:
               -S "$GITHUB_WORKSPACE" -B "$RUNNER_TEMP"
         echo "dokitVersion=$(cat "$RUNNER_TEMP/version.txt")" | tee -a "$GITHUB_OUTPUT"
         { echo -n 'tap='; [[ '${{ matrix.qt }}' =~ ^5\.1[2-9]|6 ]] && echo true || echo false; } | tee -a "$GITHUB_OUTPUT"
+        exit 1 # \todo Bow out early for now.
         cmake --build "$RUNNER_TEMP" -- VERBOSE=1
         find "$RUNNER_TEMP" -name 'Info.plist'
         find "$RUNNER_TEMP" -name 'Info.plist' -execdir cat '{}' \;