Free macOS Disk Space Only When the Build Might Not Fit (#16364)

.github/workflows/build_orca.yml

@@ -179,6 +179,13 @@ jobs:
         if: runner.os == 'macOS' && !inputs.macos-combine-only && !vars.SELF_HOSTED
         run: |
           df -hI /
+          # Deleting the unused Xcodes takes minutes, so only do it when the
+          # build might not fit. A cold build uses under 4 GiB after this step.
+          avail_gib=$(df -g / | awk 'NR == 2 { print $4 }')
+          if [ "$avail_gib" -ge 15 ]; then
+            echo "$avail_gib GiB free, enough for the build"
+            exit 0
+          fi
           # Keep only the selected Xcode
           xcode=$(basename "$(cd "$(xcode-select -p)/../.." && pwd -P)")
           sudo find /Applications -maxdepth 1 -type d -name "Xcode_*.app" ! -name "$xcode" -exec rm -rf {} +