PR libstdc++/49204
	* include/std/future (__future_base::_State_base::wait()): Use lambda
	expression for predicate and remove redundant test.
	(__future_base::_State_base::wait_for()): Return future_status and
	use lambda expression for predicate.
	(__future_base::_State_base::wait_until()): Likewise.
	(__basic_future::wait_for(), __basic_future::wait_until()): Likewise.
	(__future_base::_Async_state): Replace with _Async_state_common
	class for non-dependent functionality and _Async_state_impl class
	template for dependent functionality.
	(__future_base::_Async_state_common::_M_join): Serialize attempts to
	join thread.
	(__future_base::_Async_state_common::_M_run_deferred): Join.
	(__future_base::_Async_state::_M_do_run): Replace with lambda.
	* src/c++11/future.cc (__future_base::_Async_state_common): Define
	destructor, so key function is in the library.
	* config/abi/pre/gnu.ver: Add exports for ~_Async_state_common.
	* testsuite/30_threads/packaged_task/members/get_future.cc: Expect
	future_status return instead of bool.
	* testsuite/30_threads/shared_future/members/wait_until.cc: Likewise.
	* testsuite/30_threads/shared_future/members/wait_for.cc: Likewise.
	* testsuite/30_threads/future/members/wait_until.cc: Likewise.
	* testsuite/30_threads/future/members/wait_for.cc: Likewise.
	* testsuite/30_threads/promise/members/set_value2.cc: Likewise.
	* testsuite/30_threads/promise/members/set_value3.cc: Likewise.
	* testsuite/30_threads/promise/members/swap.cc: Likewise.

From-SVN: r183788