FileManager: support querying file ids on Windows

The moral equivalent to the inode is the FileID on Windows.  Populate
this properly into the FileInfo response from FileManager.  This was
identified by a failure in the swift-driver test suite failing to
recursively resolve response files.

Sources/Foundation/FileManager+Win32.swift

@@ -740,6 +740,12 @@ extension FileManager {
     }
 
     internal func _lstatFile(atPath path: String, withFileSystemRepresentation fsRep: UnsafePointer<NativeFSRCharType>? = nil) throws -> stat {
+        let (stbuf, _) = try _statxFile(atPath: path, withFileSystemRepresentation: fsRep)
+        return stbuf
+    }
+
+    // FIXME(compnerd) the UInt64 should be UInt128 to uniquely identify the file across volumes
+    internal func _statxFile(atPath path: String, withFileSystemRepresentation fsRep: UnsafePointer<NativeFSRCharType>? = nil) throws -> (stat, UInt64) {
         let _fsRep: UnsafePointer<NativeFSRCharType>
         if fsRep == nil {
             _fsRep = try __fileSystemRepresentation(withPath: path)
@@ -771,7 +777,8 @@ extension FileManager {
         statInfo.st_atime = info.ftLastAccessTime.time_t
         statInfo.st_ctime = info.ftCreationTime.time_t
         statInfo.st_dev = info.dwVolumeSerialNumber
-        // inodes have meaning on FAT/HPFS/NTFS
+        // The inode, and therefore st_ino, has no meaning in the FAT, HPFS, or
+        // NTFS file systems. -- docs.microsoft.com
         statInfo.st_ino = 0
         statInfo.st_rdev = info.dwVolumeSerialNumber
 
@@ -795,7 +802,8 @@ extension FileManager {
         statInfo.st_size = Int32(info.nFileSizeLow)
         // Uid is always 0 on Windows systems
         statInfo.st_uid = 0
-        return statInfo
+
+        return (statInfo, UInt64(info.nFileIndexHigh << 32) | UInt64(info.nFileIndexLow))
     }
 
     internal func _contentsEqual(atPath path1: String, andPath path2: String) -> Bool {

Sources/Foundation/FileManager.swift

@@ -538,6 +538,9 @@ open class FileManager : NSObject {
 #if os(Linux)
         let (s, creationDate) = try _statxFile(atPath: path)
         result[.creationDate] = creationDate
+#elseif os(Windows)
+        let (s, ino) = try _statxFile(atPath: path)
+        result[.creationDate] = s.creationDate
 #else
         let s = try _lstatFile(atPath: path)
         result[.creationDate] = s.creationDate
@@ -553,7 +556,11 @@ open class FileManager : NSObject {
         result[.posixPermissions] = NSNumber(value: _filePermissionsMask(mode: UInt32(s.st_mode)))
         result[.referenceCount] = NSNumber(value: UInt64(s.st_nlink))
         result[.systemNumber] = NSNumber(value: UInt64(s.st_dev))
+#if os(Windows)
+        result[.systemFileNumber] = NSNumber(value: UInt64(ino))
+#else
         result[.systemFileNumber] = NSNumber(value: UInt64(s.st_ino))
+#endif
 
 #if os(Windows)
         result[.deviceIdentifier] = NSNumber(value: UInt64(s.st_rdev))