libstdc++: Fix two tests that fail in C++20 mode

	* testsuite/20_util/is_constructible/value-2.cc: Fix test to account
	for changes due to parenthesized aggregate-initialization in C++20.
	* testsuite/20_util/time_point/cons/81468.cc: Fix test to not clash
	with std::chrono::sys_time in C++20.

libstdc++-v3/ChangeLog

 2020-03-28  Jonathan Wakely  <jwakely@redhat.com>
 
+	* testsuite/20_util/is_constructible/value-2.cc: Fix test to account
+	for changes due to parenthesized aggregate-initialization in C++20.
+	* testsuite/20_util/time_point/cons/81468.cc: Fix test to not clash
+	with std::chrono::sys_time in C++20.
+
 	* include/bits/stl_iterator.h (reverse_iterator): Use requires-clause
 	to constrain C++20 versions of comparison operators. Fix backwards
 	logic of relational operators.

libstdc++-v3/testsuite/20_util/is_constructible/value-2.cc

@@ -107,7 +107,9 @@ static_assert(!std::is_constructible<Abstract, std::nullptr_t>::value, "Error");
 static_assert(!std::is_constructible<std::nullptr_t, Abstract>::value, "Error");
 static_assert(!std::is_constructible<Abstract, int[]>::value, "Error");
 static_assert(std::is_constructible<B, D>::value, "Error");
+#ifndef __cpp_aggregate_paren_init
 static_assert(!std::is_constructible<D, B>::value, "Error");
+#endif
 static_assert(!std::is_constructible<int[], int[1]>::value, "Error");
 static_assert(!std::is_constructible<int[1], int[]>::value, "Error");
 static_assert(!std::is_constructible<int[], Empty>::value, "Error");
@@ -416,7 +418,9 @@ static_assert(!std::is_constructible<int(&)[1], int(&)[2]>::value, "Error");
 static_assert(!std::is_constructible<int(&)[1], int&>::value, "Error");
 static_assert(!std::is_constructible<int&, int(&)[1]>::value, "Error");
 
+#ifndef __cpp_aggregate_paren_init
 static_assert(!std::is_constructible<U, int>::value, "Error");
+#endif
 static_assert(!std::is_constructible<U, Empty>::value, "Error");
 
 static_assert(!std::is_constructible<void(), void()>::value, "Error");

libstdc++-v3/testsuite/20_util/time_point/cons/81468.cc

@@ -20,11 +20,13 @@
 #include <chrono>
 #include <type_traits>
 
-using namespace std;
-using namespace std::chrono;
+using std::is_constructible;
+using std::chrono::seconds;
+using std::chrono::milliseconds;
 
 template <class Duration>
-    using sys_time = time_point<system_clock, Duration>;
+    using sys_time
+      = std::chrono::time_point<std::chrono::system_clock, Duration>;
 
 static_assert(is_constructible<sys_time<milliseconds>, sys_time<seconds>>{},
     "Can construct time_point from one with lower precision duration");