libstdc++: Define __cpp_lib_constexpr_complex macro

This is LWG issue 3349.

	* include/std/complex (__cpp_lib_constexpr_complex): Define.
	* include/std/version (__cpp_lib_constexpr_complex): Likewise.
	* testsuite/26_numerics/complex/1.cc: New test.
	* testsuite/26_numerics/complex/2.cc: New test.

From-SVN: r279172

libstdc++-v3/ChangeLog

 2019-12-10  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/complex (__cpp_lib_constexpr_complex): Define.
+	* include/std/version (__cpp_lib_constexpr_complex): Likewise.
+	* testsuite/26_numerics/complex/1.cc: New test.
+	* testsuite/26_numerics/complex/2.cc: New test.
+
 	* include/std/span: Do not include <tuple> and <utility>.
 	(tuple_size, tuple_element): Declare.
 

libstdc++-v3/include/std/complex

@@ -47,6 +47,10 @@
 // Get rid of a macro possibly defined in <complex.h>
 #undef complex
 
+#if __cplusplus > 201703L
+# define __cpp_lib_constexpr_complex 201711L
+#endif
+
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION

libstdc++-v3/include/std/version

@@ -180,6 +180,7 @@
 #if _GLIBCXX_HOSTED
 #define __cpp_lib_bind_front 201907L
 #define __cpp_lib_constexpr_algorithms 201806L
+#define __cpp_lib_constexpr_complex 201711L
 #define __cpp_lib_constexpr_dynamic_alloc 201907L
 #define __cpp_lib_constexpr_invoke 201907L
 #define __cpp_lib_erase_if 201900L

libstdc++-v3/testsuite/26_numerics/complex/1.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do preprocess { target c++2a } }
+
+#include <complex>
+
+#ifndef __cpp_lib_constexpr_complex
+# error "Feature test macro for constexpr complex is missing in <complex>"
+#elif __cpp_lib_constexpr_complex < 201711L
+# error "Feature test macro for constexpr complex has wrong value in <complex>"
+#endif

libstdc++-v3/testsuite/26_numerics/complex/2.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do preprocess { target c++2a } }
+
+#include <version>
+
+#ifndef __cpp_lib_constexpr_complex
+# error "Feature test macro for constexpr complex is missing in <version>"
+#elif __cpp_lib_constexpr_complex < 201711L
+# error "Feature test macro for constexpr complex has wrong value in <version>"
+#endif