stdlib: better type for WinSDK constant

Alter the constant type for the FileOperationFlag type.  This allows the
type system check the paramter type better.

Author: compnerd

stdlib/public/Windows/WinSDK.swift

@@ -34,6 +34,6 @@ public let TRUE: BOOL = 1
 public let INVALID_HANDLE_VALUE: HANDLE = HANDLE(bitPattern: -1)!
 
 // shellapi.h
-public let FOF_NO_UI: DWORD =
-    DWORD(FOF_SILENT | FOF_NOCONFIRMATION | FOF_NOERRORUI | FOF_NOCONFIRMMKDIR)
+public let FOF_NO_UI: FILEOP_FLAGS =
+    FILEOP_FLAGS(FOF_SILENT | FOF_NOCONFIRMATION | FOF_NOERRORUI | FOF_NOCONFIRMMKDIR)