Use pthread effective-target in testsuite

	* testsuite: Add dg-require-effective-target pthread to -pthread
	tests.
	Remove explicit target lists from dg-do and dg-options.

	* testsuite/30_threads/async/forced_unwind.cc: Remove explit
	target list from dg-options.
	* testsuite/30_threads/packaged_task/forced_unwind.cc: Likewise.

	* 30_threads/shared_mutex/cons/1.cc: Likewise.
	Pass -pthread for all targets.
	* 30_threads/shared_mutex/try_lock/1.cc: Likewise.
	* 30_threads/shared_mutex/try_lock/2.cc: Likewise.
	* 30_threads/shared_mutex/unlock/1.cc: Likewise.

	* testsuite/30_threads/this_thread/57060.cc: Require c++11 via
	dg-require-effective-target.

From-SVN: r249217