* include/bits/parse_numbers.h (__parse_int::_Number_help): Check for
	overflow.
	* include/std/chrono (chrono_literals::__select_type::_Select_type):
	Remove.
	(chrono_literals::_Checked_integral_constant): Define.
	Simplify UDL operator templates and check for overflow.
	* testsuite/20_util/duration/literals/range.cc: New.

From-SVN: r210513