libstdc++: Test C++11 implementation of std::chrono::__detail::ceil

Commit 53ad6b1979f4bd7121e977c4a44151b14d8a0147 split the implementation
of std::chrono::__detail::ceil so that when compiling for C++17 and
later std::chrono::ceil is used but when compiling for earlier versions
a separate implementation is used to comply with C++11's limited
constexpr rules. Let's run the equivalent of the existing
std::chrono::ceil test cases on std::chrono::__detail::ceil too to make
sure that it doesn't get broken.

libstdc++-v3/ChangeLog:

	* testsuite/20_util/duration_cast/rounding_c++11.cc: Copy
	rounding.cc and alter to support compilation for C++11 and to
	test std::chrono::__detail::ceil.

1 files changed, 43 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/20_util/duration_cast/rounding_c++11.cc b/libstdc++-v3/testsuite/20_util/duration_cast/rounding_c++11.cc
new file mode 100644
index 0000000..f10d27f
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/duration_cast/rounding_c++11.cc
@@ -0,0 +1,43 @@
+// Copyright (C) 2016-2020 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++11" }
+// { dg-do compile { target c++11 } }
+
+#include <chrono>
+
+using std::chrono::seconds;
+using std::chrono::milliseconds;
+
+using fp_seconds = std::chrono::duration<float>;
+
+static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(1000))
+	       == seconds(1) );
+static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(1001))
+	       == seconds(2) );
+static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(1500))
+	       == seconds(2) );
+static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(1999))
+	       == seconds(2) );
+static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(2000))
+	       == seconds(2) );
+static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(2001))
+	       == seconds(3) );
+static_assert( std::chrono::__detail::ceil<seconds>(milliseconds(2500))
+	       == seconds(3) );
+static_assert( std::chrono::__detail::ceil<fp_seconds>(milliseconds(500))
+	       == fp_seconds{0.5f} );