title: Try to build swift from master branch failed
body: <p>swift/stdlib/public/SDK/SafariServices/SafariServices.swift:14:8: error: could not build Objective-C module '_SwiftSafariServicesOverlayShims' import <em>SwiftSafariServicesOverlayShims        ^ [19/388] Compiling build...vate/SwiftPrivateLibcExtras/macosx/x86</em></p>
  
  <p>The module _SwiftSafariServicesOverlayShims seems to be in beta Max OS 10.12.4,  I installed it and still not working( ./utils/build-script -r -t). Cannot figure out why</p>