A symbol starting with two leading underscores is reserved for
the compiler/standard library implementation.

Also remove the trailing two double underscores for consistency
and symmetry.

With minor contributions from:
 - Jean-Baptiste Kempf <jb@videolan.org>
 - Marvin Scholz <epirat07@gmail.com>
 - Hugo Beauzée-Luyssen <hugo@videolan.org>