libstdc++: Fix for explicit copy ctors in <thread> and <future> [PR106695]

When I changed std::thread and std::async to avoid unnecessary move
construction of temporaries, I introduced a regression where types with
an explicit copy constructor could not be passed to std::thread or
std::async. The fix is to add a constructor instead of using aggregate
initialization of an unnamed temporary.

libstdc++-v3/ChangeLog:

	PR libstdc++/106695
	* include/bits/std_thread.h (thread::_State_impl): Forward
	individual arguments to _Invoker constructor.
	(thread::_Invoker): Add constructor. Delete copies.
	* include/std/future (__future_base::_Deferred_state): Forward
	individual arguments to _Invoker constructor.
	(__future_base::_Async_state_impl): Likewise.
	* testsuite/30_threads/async/106695.cc: New test.
	* testsuite/30_threads/thread/106695.cc: New test.

libstdc++-v3/include/bits/std_thread.h

@@ -227,7 +227,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 	template<typename... _Args>
 	  _State_impl(_Args&&... __args)
-	  : _M_func{{std::forward<_Args>(__args)...}}
+	  : _M_func(std::forward<_Args>(__args)...)
 	  { }
 
 	void
@@ -261,6 +261,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _Tuple>
       struct _Invoker
       {
+	template<typename... _Args>
+	  explicit
+	  _Invoker(_Args&&... __args)
+	  : _M_t(std::forward<_Args>(__args)...)
+	  { }
+
 	_Tuple _M_t;
 
 	template<typename>

libstdc++-v3/include/std/future

@@ -1681,7 +1681,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	explicit
 	_Deferred_state(_Args&&... __args)
 	: _M_result(new _Result<_Res>()),
-	  _M_fn{{std::forward<_Args>(__args)...}}
+	  _M_fn(std::forward<_Args>(__args)...)
 	{ }
 
     private:
@@ -1748,7 +1748,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	explicit
 	_Async_state_impl(_Args&&... __args)
 	: _M_result(new _Result<_Res>()),
-	  _M_fn{{std::forward<_Args>(__args)...}}
+	  _M_fn(std::forward<_Args>(__args)...)
 	{
 	  _M_thread = std::thread{&_Async_state_impl::_M_run, this};
 	}

libstdc++-v3/testsuite/30_threads/async/106695.cc

@@ -0,0 +1,29 @@
+// { dg-do compile { target c++11 } }
+// { dg-require-gthreads "" }
+
+// PR libstdc++/106695
+// Explicit copy constructor does not work for a parameter passed via std::async
+
+#include <future>
+
+struct A {
+  A() = default;
+  explicit A(const A&) = default;
+};
+
+void func(const A&) { }
+
+void
+test_async()
+{
+  (void) std::async(std::launch::async, func, A{});
+  (void) std::async(std::launch::deferred, func, A{});
+  (void) std::async(func, A{});
+}
+
+void
+test_task()
+{
+  std::packaged_task<void(const A&)> task(func);
+  task(A{});
+}

libstdc++-v3/testsuite/30_threads/thread/106695.cc

@@ -0,0 +1,21 @@
+// { dg-do compile { target c++11 } }
+// { dg-require-gthreads "" }
+
+// PR libstdc++/106695
+// Explicit copy constructor does not work for a parameter passed via std::async
+
+#include <thread>
+
+struct A {
+  A() = default;
+  explicit A(const A&) = default;
+};
+
+void func(const A&) { }
+
+void
+test_thread()
+{
+  std::thread t(func, A{});
+  t.join();
+}