2017-02-19  Dinka Ranns  <dinka.ranns@googlemail.com>

	C++17 GB50 resolution
	* include/std/chrono (duration::operator++()): Add
	_GLIBCXX17_CONSTEXPR.
	(duration::operator++(int)): Likewise.
	(duration::operator--()): Likewise.
	(duration::operator--(int)): Likewise.
	(duration::operator+=(const duration&)): Likewise.
	(duration::operator-=(const duration&)): Likewise.
	(duration::operator*=(const rep&)): Likewise.
	(duration::operator/=(const rep&)): Likewise.
	(duration::operator%=(const rep&)): Likewise.
	(duration::operator%=(const duration&)): Likewise.
	(time_point::operator+=(const duration&)): Likewise.
	(time_point::operator-=(const duration&)): Likewise.
	* testsuite/20_util/duration/arithmetic/constexpr_c++17.cc: New test.
	* testsuite/20_util/duration/literals/range.cc: Adjust dg-error.
	* testsuite/20_util/time_point/arithmetic/constexpr.cc: New test.

From-SVN: r245575