Foundation: initialize CFSocket on startup

Windows requires the networking subsystem (WinSock) to be initialized.
However, the user expects to be able to use the networking APIs in
Foundation without performing any one-time initialization.  Furthermore,
due to the macro usage in the initialization path, it is easier to
perform the initialization in C than in Swift.  CoreFoundation has a SPI
for this (`__CFSocketInitializeWinSock`).

Author: compnerd

Foundation/NSSwiftRuntime.swift

@@ -147,10 +147,18 @@ internal func __CFSwiftGetBaseClass() -> UnsafeRawPointer {
     return unsafeBitCast(__NSCFType.self, to:UnsafeRawPointer.self)
 }
 
+#if os(Windows)
+@_silgen_name("__CFSocketInitializeWinSock")
+func __CFSocketInitializeWinSock() -> ()
+#endif
+
 @usableFromInline
 @_cdecl("__CFInitializeSwift")
 internal func __CFInitializeSwift() {
-    
+#if os(Windows)
+    __CFSocketInitializeWinSock()
+#endif
+
     _CFRuntimeBridgeTypeToClass(CFStringGetTypeID(), unsafeBitCast(_NSCFString.self, to: UnsafeRawPointer.self))
     _CFRuntimeBridgeTypeToClass(CFArrayGetTypeID(), unsafeBitCast(_NSCFArray.self, to: UnsafeRawPointer.self))
     _CFRuntimeBridgeTypeToClass(CFDictionaryGetTypeID(), unsafeBitCast(_NSCFDictionary.self, to: UnsafeRawPointer.self))