Closes https://github.com/CocoaPods/CocoaPods/issues/3813.

[Executable] Dont use a subprocess for which

[Installer] Improve error message when using Swift in static libs.

Now it includes the offending Pods so that the user can take action
to remove the Pods, if they don’t want to move to frameworks yet.

Add a flag in the git attributes to do union merges

[CHANGELOG] Add a flag in the git attributes to do union merges, always saving both lines in the note

[Specs] Fixed plugin specs in the incorrect files

[Resolver] Make verbose resolution less so

[Installer] Ensure no duplicate target deps are created

[Integration] Fix cleaning of plugin paths

[XCConfig] Only include -ObjC flag when linking against a static lib