proper OS-dependent declaration of protocol conformance for DispatchSource

Author: dgrove-oss

src/swift/Wrapper.swift

@@ -139,8 +139,6 @@ public class DispatchQueue : DispatchObject {
 	}
 }
 
-// FIXME: the list of implemented protocols is OS dependent.
-//        need to properly conditionalize this declaration.
 public class DispatchSource : DispatchObject,
 	DispatchSourceType,	DispatchSourceRead,
 	DispatchSourceSignal, DispatchSourceTimer,
@@ -157,6 +155,18 @@ public class DispatchSource : DispatchObject,
 	}
 }
 
+#if HAVE_MACH
+extension DispatchSource : DispatchSourceMachSend,
+	DispatchSourceMachReceive, DispatchSourceMemoryPressure {
+}
+#endif
+
+#if !os(Linux)
+extension DispatchSource : DispatchSourceProcess,
+	DispatchSourceFileSystemObject {
+}
+#endif
+
 public protocol DispatchSourceType {
 #if false // crashes the swift compiler
   typealias DispatchSourceHandler = @convention(block) () -> Void