Define std::enable_shared_from_this::weak_from_this

	* testsuite/20_util/enable_shared_from_this/members/reinit.cc: Use
	effective target not dg-options. Move check for feature-test macro to:
	* testsuite/20_util/enable_shared_from_this/members/weak_from_this.cc:
	New test.

From-SVN: r239121

libstdc++-v3/ChangeLog

 2016-08-04  Jonathan Wakely  <jwakely@redhat.com>
 
+	* testsuite/20_util/enable_shared_from_this/members/reinit.cc: Use
+	effective target not dg-options. Move check for feature-test macro to:
+	* testsuite/20_util/enable_shared_from_this/members/weak_from_this.cc:
+	New test.
+
 	* include/std/functional (_Unwrap): Rename to __inv_unwrap.
 	(__invfwd): Adjust.
 	(__invoke_impl): Remove unused template parameters.

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

@@ -586,6 +586,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       shared_from_this() const
       { return shared_ptr<const _Tp>(this->_M_weak_this); }
 
+#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
+#define __cpp_lib_enable_shared_from_this 201603
+      weak_ptr<_Tp>
+      weak_from_this()
+      { return this->_M_weak_this; }
+
+      weak_ptr<const _Tp>
+      weak_from_this() const
+      { return this->_M_weak_this; }
+#endif
+
     private:
       template<typename _Tp1>
 	void

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

@@ -1472,7 +1472,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       void
       _M_assign(_Tp* __ptr, const __shared_count<_Lp>& __refcount) noexcept
       {
-#define __cpp_lib_enable_shared_from_this 201603
 	if (use_count() == 0)
 	  {
 	    _M_ptr = __ptr;
@@ -1557,6 +1556,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       shared_from_this() const
       { return __shared_ptr<const _Tp, _Lp>(this->_M_weak_this); }
 
+#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
+      __weak_ptr<_Tp, _Lp>
+      weak_from_this()
+      { return this->_M_weak_this; }
+
+      __weak_ptr<const _Tp, _Lp>
+      weak_from_this() const
+      { return this->_M_weak_this; }
+#endif
+
     private:
       template<typename _Tp1>
 	void

libstdc++-v3/testsuite/20_util/enable_shared_from_this/members/reinit.cc

@@ -15,15 +15,11 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// { dg-options "-std=gnu++11" }
+// { dg-do run { target c++11 } }
 
 #include <memory>
 #include <testsuite_hooks.h>
 
-#if __cpp_lib_enable_shared_from_this < 201603
-# error "__cpp_lib_enable_shared_from_this < 201603"
-#endif
-
 struct X : public std::enable_shared_from_this<X> { };
 
 bool