[ModuleMapGeneration] Add modulemap link declaration support to modulemap generation.
[ModuleMapGeneration] Add modulemap link declaration support to modulemap generation.

This will help in autolinking when using frameworks for Xcode targets.

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