Implement void_t from N3911. Add a private version for use in the library before C++1z. Update the 1z status page, marking a bunch of issues that don't require library changes as complete (2129, 2212, 2230, 2233, 2325, 2365, 2376)

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@222138 91177308-0d34-0410-b5e6-96231b3b80d8

test/utilities/meta/meta.unary.prop.query/void_t.pass.cpp

@@ -0,0 +1,69 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// type_traits
+
+// void_t
+
+#include <type_traits>
+
+#if _LIBCPP_STD_VER <= 14
+int main () {}
+#else
+
+template <class T>
+void test1()
+{
+    static_assert( std::is_same<void, std::void_t<T>>::value, "");
+    static_assert( std::is_same<void, std::void_t<const T>>::value, "");
+    static_assert( std::is_same<void, std::void_t<volatile T>>::value, "");
+    static_assert( std::is_same<void, std::void_t<const volatile T>>::value, "");
+}
+
+template <class T, class U>
+void test2()
+{
+    static_assert( std::is_same<void, std::void_t<T, U>>::value, "");
+    static_assert( std::is_same<void, std::void_t<const T, U>>::value, "");
+    static_assert( std::is_same<void, std::void_t<volatile T, U>>::value, "");
+    static_assert( std::is_same<void, std::void_t<const volatile T, U>>::value, "");
+
+    static_assert( std::is_same<void, std::void_t<T, const U>>::value, "");
+    static_assert( std::is_same<void, std::void_t<const T, const U>>::value, "");
+    static_assert( std::is_same<void, std::void_t<volatile T, const U>>::value, "");
+    static_assert( std::is_same<void, std::void_t<const volatile T, const U>>::value, "");
+}
+
+class Class
+{
+public:
+    ~Class();
+};
+
+int main()
+{
+    static_assert( std::is_same<void, std::void_t<>>::value, "");
+
+	test1<void>();
+	test1<int>();
+	test1<double>();
+	test1<int&>();
+	test1<Class>();
+	test1<Class[]>();
+	test1<Class[5]>();
+	
+	test2<void, int>();
+	test2<double, int>();
+	test2<int&, int>();
+	test2<Class&, bool>();
+	test2<void *, int&>();
+
+    static_assert( std::is_same<void, std::void_t<int, double const &, Class, volatile int[], void>>::value, "");
+}
+#endif