Steps to reproduce

1. Create a Flutter project with iOS support
2. Add CocoaPods dependencies (Firebase, etc.)
3. Run pod install in the ios directory
4. Open the project in Xcode
5. Attempt to archive the project (Product → Archive)
6. Build fails with "Improperly formatted define flag" error

Expected results

The archive should complete successfully, as it does in Flutter 3.35.7.

Actual results

Archive build fails with the following error:

Improperly formatted define flag: Failed to package /path/to/project.
Command PhaseScriptExecution failed with a nonzero exit code

The error occurs during the "Run Script" build phase that executes:

/bin/sh "$FLUTTER_ROOT/packages/flutter_tools/bin/xcode_backend.sh" build

Build Log Details

The build log shows that OTHER_SWIFT_FLAGS and GCC_PREPROCESSOR_DEFINITIONS are being expanded with leading spaces:

export OTHER_SWIFT_FLAGS\=\ -DCOCOAPODS
export GCC_PREPROCESSOR_DEFINITIONS\=\  COCOAPODS=1 ...

Note the double space after the = sign, which appears to be causing the Flutter build script to fail.

Additional Context

• No code changes were made between testing 3.35.7 and 3.38.0
• The issue appears to be related to how Flutter 3.38.0's xcode_backend.sh script processes build settings with define flags
• The error specifically occurs during the archive process, not during regular builds
• The project uses CocoaPods with dependencies including Firebase, VeriffSDK, and other iOS frameworks

Code sample

[Paste your code here]

Screenshots or Video

Logs

Improperly formatted define flag: Failed to package /path/to/project.
Command PhaseScriptExecution failed with a nonzero exit code

/bin/sh "$FLUTTER_ROOT/packages/flutter_tools/bin/xcode_backend.sh" build

export OTHER_SWIFT_FLAGS\=\ -DCOCOAPODS
export GCC_PREPROCESSOR_DEFINITIONS\=\  COCOAPODS=1 ...

Flutter Doctor output

[✓] Flutter (Channel stable, 3.38.0, on macOS 26.1 25B78 darwin-arm64, locale
    en-US)
[✓] Android toolchain - develop for Android devices (Android SDK version 36.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 26.1.1)
[✓] Chrome - develop for the web
[✓] Connected device (3 available)
[✓] Network resources

• No issues found!