flutter335: fix macos build

Fix for macOS build issue in Flutter >= 3.35

Since version 3.35, the behavior of macos_assemble.sh and xcode_backend.sh

is almost identical. This caused the same error for macOS that previously

occurred for iOS.

Derived from the iOS patch: ./fix-ios-build-xcode-backend-sh.patch

Example error:

```

$ flutter run -d macos

Launching lib/main.dart on macOS in debug mode...

Target debug_unpack_macos failed: Error: Flutter failed to create a directory at "/<nix-store>/XXXX-flutter-3.35.1-unwrapped/bin/cache/artifacts".

Please ensure that the SDK and/or project is installed in a location that has read/write permissions for the current user.

Failed to copy Flutter framework.

** BUILD FAILED **

```

---

diff --git a/packages/flutter_tools/bin/macos_assemble.sh b/packages/flutter_tools/bin/macos_assemble.sh

index 28acf8842..d0f2923df 100644

--- a/packages/flutter_tools/bin/macos_assemble.sh

+++ b/packages/flutter_tools/bin/macos_assemble.sh

@@ -13,29 +13,13 @@

 # exit on error, or usage of unset var

 set -euo pipefail

-# Needed because if it is set, cd may print the path it changed to.

-unset CDPATH

-

-function follow_links() (

-  cd -P "$(dirname -- "$1")"

-  file="$PWD/$(basename -- "$1")"

-  while [[ -h "$file" ]]; do

-    cd -P "$(dirname -- "$file")"

-    file="$(readlink -- "$file")"

-    cd -P "$(dirname -- "$file")"

-    file="$PWD/$(basename -- "$file")"

-  done

-  echo "$file"

-)

-

-PROG_NAME="$(follow_links "${BASH_SOURCE[0]}")"

-BIN_DIR="$(cd "${PROG_NAME%/*}" ; pwd -P)"

-FLUTTER_ROOT="$BIN_DIR/../../.."

-DART="$FLUTTER_ROOT/bin/dart"

+# Run `dart ./xcode_backend.dart` with the dart from $FLUTTER_ROOT.

+dart="${FLUTTER_ROOT}/bin/dart"

+xcode_backend_dart="$(dirname "${BASH_SOURCE[0]}")/xcode_backend.dart"

 # Main entry point.

 if [[ $# == 0 ]]; then

-  "$DART" "$BIN_DIR/xcode_backend.dart" "build" "macos"

+  exec "${dart}" "${xcode_backend_dart}" "build" "macos"

 else

-  "$DART" "$BIN_DIR/xcode_backend.dart" "$@" "macos"

+  exec "${dart}" "${xcode_backend_dart}" "$@" "macos"

 fi