Fixing internal type visibility

Source commit: 375d6ff91122bae579363d4e2064e680050e37ab

dotnet/internal/UnsafeNativeMethods.cs

@@ -74,7 +74,7 @@ namespace WinSCP
     }
 
     [Flags]
-    public enum FileMapAccess : int
+    internal enum FileMapAccess : int
     {
         FileMapCopy = 0x0001,
         FileMapWrite = 0x0002,