libstdc++: Make comparison category comparisons noexcept (PR 94565)

	PR libstdc++/94565
	* libsupc++/compare (__unspec): Add noexcept-specifier to constructor.
	* testsuite/18_support/comparisons/categories/94565.cc: New test.

libstdc++-v3/ChangeLog

@@ -3,6 +3,12 @@
 	* include/std/coroutine: Update coroutines builtin define,
 	per n4861.
 
+2020-04-14  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/94565
+	* libsupc++/compare (__unspec): Add noexcept-specifier to constructor.
+	* testsuite/18_support/comparisons/categories/94565.cc: New test.
+
 2020-04-09  Jonathan Wakely  <jwakely@redhat.com>
 
 	* libsupc++/compare (compare_three_way): Fix noexcept-specifier.

libstdc++-v3/libsupc++/compare

@@ -56,7 +56,7 @@ namespace std
 
     struct __unspec
     {
-      constexpr __unspec(__unspec*) { }
+      constexpr __unspec(__unspec*) noexcept { }
     };
   }
 

libstdc++-v3/testsuite/18_support/comparisons/categories/94565.cc

+// Copyright (C) 2020 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 compile { target c++2a } }
+
+#include <compare>
+
+static_assert(noexcept(std::partial_ordering::less == 0));
+static_assert(noexcept(std::partial_ordering::less != 0));
+static_assert(noexcept(std::partial_ordering::less < 0));
+static_assert(noexcept(std::partial_ordering::less > 0));
+static_assert(noexcept(std::partial_ordering::less <= 0));
+static_assert(noexcept(std::partial_ordering::less >= 0));
+static_assert(noexcept(std::partial_ordering::less <=> 0));
+static_assert(noexcept(0 == std::partial_ordering::less));
+static_assert(noexcept(0 != std::partial_ordering::less));
+static_assert(noexcept(0 < std::partial_ordering::less));
+static_assert(noexcept(0 > std::partial_ordering::less));
+static_assert(noexcept(0 <= std::partial_ordering::less));
+static_assert(noexcept(0 >= std::partial_ordering::less));
+static_assert(noexcept(0 <=> std::partial_ordering::less));
+
+static_assert(noexcept(std::weak_ordering::less == 0));
+static_assert(noexcept(std::weak_ordering::less != 0));
+static_assert(noexcept(std::weak_ordering::less < 0));
+static_assert(noexcept(std::weak_ordering::less > 0));
+static_assert(noexcept(std::weak_ordering::less <= 0));
+static_assert(noexcept(std::weak_ordering::less >= 0));
+static_assert(noexcept(std::weak_ordering::less <=> 0));
+static_assert(noexcept(0 == std::weak_ordering::less));
+static_assert(noexcept(0 != std::weak_ordering::less));
+static_assert(noexcept(0 < std::weak_ordering::less));
+static_assert(noexcept(0 > std::weak_ordering::less));
+static_assert(noexcept(0 <= std::weak_ordering::less));
+static_assert(noexcept(0 >= std::weak_ordering::less));
+static_assert(noexcept(0 <=> std::weak_ordering::less));
+
+static_assert(noexcept(std::strong_ordering::less == 0));
+static_assert(noexcept(std::strong_ordering::less != 0));
+static_assert(noexcept(std::strong_ordering::less < 0));
+static_assert(noexcept(std::strong_ordering::less > 0));
+static_assert(noexcept(std::strong_ordering::less <= 0));
+static_assert(noexcept(std::strong_ordering::less >= 0));
+static_assert(noexcept(std::strong_ordering::less <=> 0));
+static_assert(noexcept(0 == std::strong_ordering::less));
+static_assert(noexcept(0 != std::strong_ordering::less));
+static_assert(noexcept(0 < std::strong_ordering::less));
+static_assert(noexcept(0 > std::strong_ordering::less));
+static_assert(noexcept(0 <= std::strong_ordering::less));
+static_assert(noexcept(0 >= std::strong_ordering::less));
+static_assert(noexcept(0 <=> std::strong_ordering::less));