https://bugs.swift.org/browse/SR-2811 Generated Xcode projects need to allow .xcconfig files to override project settings
https://bugs.swift.org/browse/SR-2811 Generated Xcode projects need to allow .xcconfig files to override project settings

This moves the layering of settings from any overriding .xcconfig file so they can override the project layer.  It also moves down some settings from the target level to the project level so they can be overridden by the .xcconfig.

apple/swift-package-manager,JGiola/swift-package-manager,sschiau/swift-package-manager,vmanot/swift-package-manager,sschiau/swift-package-manager,vmanot/swift-package-manager,apple/swift-package-manager,JGiola/swift-package-manager,sschiau/swift-package-manager,sschiau/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,vmanot/swift-package-manager,vmanot/swift-package-manager,JGiola/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,JGiola/swift-package-manager,JGiola/swift-package-manager,vmanot/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,sschiau/swift-package-manager