PR libstdc++/89461
	* testsuite/lib/libstdc++.exp: Locate libatomic.
	* testsuite/lib/dg-options.exp (add_options_for_libatomic): New.
	* testsuite/20_util/shared_ptr/thread/default_weaktoshared.cc: Add
	libatomic options.
	* testsuite/20_util/shared_ptr/thread/mutex_weaktoshared.cc: Likewise.
	* testsuite/experimental/net/timer/waitable/cons.cc: Likewise.
	* testsuite/experimental/net/timer/waitable/dest.cc: Likewise.
	* testsuite/experimental/net/timer/waitable/ops.cc: Likewise.

From-SVN: r269628