mutex (once_flag): Construct __gthread_once_t in a temporary variable before assigning to _M_once...

2008-09-04  Chris Fairles  <chris.fairles@gmail.com>

        * include/std/mutex (once_flag): Construct __gthread_once_t in a
	temporary variable before assigning to _M_once to avoid initialization
	errors.

From-SVN: r139986