[bootstrap] Write proper xcconfig if linking llbuild
[bootstrap] Write proper xcconfig if linking llbuild

This makes the generated Xcode project work when we link llbuild

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