Fix a Linux-specific compilation error.
Fix a Linux-specific compilation error.

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