Ensure this doesn't break the Windows build

- HANDLE was being picked up transitively by CF's reexporting; import it explicitly
- There was one CF type in a stored property in a #if os(Windows) block.

Author: millenomi

Sources/Foundation/FileHandle.swift

@@ -24,6 +24,13 @@ fileprivate let _write = Glibc.write(_:_:_:)
 fileprivate let _close = Glibc.close(_:)
 #endif
 
+#if canImport(WinSDK)
+// We used to get the copy that was re-exported by CoreFoundation
+// but we want to explicitly depend on its types in this file,
+// so we need to make sure Swift doesn't think it's @_implementationOnly.
+import WinSDK
+#endif
+
 extension NSError {
     internal var errnoIfAvailable: Int? {
         if domain == NSPOSIXErrorDomain {

Sources/Foundation/Process.swift

@@ -13,6 +13,13 @@
 import Darwin
 #endif
 
+#if canImport(WinSDK)
+// We used to get the copy that was re-exported by CoreFoundation
+// but we want to explicitly depend on its types in this file,
+// so we need to make sure Swift doesn't think it's @_implementationOnly.
+import WinSDK
+#endif
+
 extension Process {
     public enum TerminationReason : Int {
         case exit

Sources/Foundation/Thread.swift

@@ -196,9 +196,17 @@ open class Thread : NSObject {
     private var _thread: _swift_CFThreadRef? = nil
 
 #if os(Windows) && !CYGWIN
-    internal var _attr: _CFThreadAttributes =
-        _CFThreadAttributes(dwSizeOfAttributes: DWORD(MemoryLayout<_CFThreadAttributes>.size),
+    private class NonexportedAttrStorage {
+        var value = _CFThreadAttributes(dwSizeOfAttributes: DWORD(MemoryLayout<_CFThreadAttributes>.size),
                             dwThreadStackReservation: 0)
+    }
+
+    private let _attrStorage = NonexportedAttrStorage()
+
+    internal var _attr: _CFThreadAttributes {
+        get { _attrStorage.value }
+        set { _attrStorage.value = newValue }
+    }
 #elseif CYGWIN
     internal var _attr : pthread_attr_t? = nil
 #else