C++: improve location of static_assert errors

C++: improve location of static_assert errors

gcc/cp/ChangeLog:
	* parser.c (cp_parser_unary_expression): Generate a location for
	"noexcept".
	(cp_parser_trait_expr): Generate and return a location_t,
	converting the return type from tree to cp_expr.
	(cp_parser_static_assert): Pass location of the condition to
	finish_static_assert, rather than that of the "static_assert"
	token, where available.

gcc/testsuite/ChangeLog:
	* g++.dg/cpp1y/static_assert3.C: New test case.

libstdc++-v3/ChangeLog:
	* testsuite/20_util/duration/literals/range.cc: Update expected
	line of a static_assert failure.

From-SVN: r255255