Keep Flutter.framework binaries writable so they can be code signed (#39539)

.cirrus.yml

@@ -532,7 +532,6 @@ task:
         - ulimit -S -n 2048 # https://github.com/flutter/flutter/issues/2976
         - dart --enable-asserts dev/bots/test.dart
     - name: add2app-macos
-      skip: true # https://github.com/flutter/flutter/issues/39507
       env:
         SHARD: add2app_test
       setup_xcpretty_script:

packages/flutter_tools/bin/xcode_backend.sh

@@ -142,11 +142,13 @@ BuildApp() {
     mkdir "${derived_dir}/engine"
     RunCommand cp -r -- "${flutter_podspec}" "${derived_dir}/engine"
     RunCommand cp -r -- "${flutter_framework}" "${derived_dir}/engine"
-    RunCommand find "${derived_dir}/engine/Flutter.framework" -type f -exec chmod a-w "{}" \;
+    # Make non-binary files read-only to discourage editing headers, but allow binary code-signing.
+    RunCommand find "${derived_dir}/engine/Flutter.framework" -type f -exec grep -Il '.' {} \; | xargs chmod a-w
   else
     RunCommand rm -rf -- "${derived_dir}/Flutter.framework"
     RunCommand cp -r -- "${flutter_framework}" "${derived_dir}"
-    RunCommand find "${derived_dir}/Flutter.framework" -type f -exec chmod a-w "{}" \;
+    # Make non-binary files read-only to discourage editing headers, but allow binary code-signing.
+    RunCommand find "${derived_dir}/Flutter.framework" -type f -exec grep -Il '.' {} \; | xargs chmod a-w
   fi
 
   RunCommand pushd "${project_path}" > /dev/null