* internal-fn.def (LAUNDER): New internal function.
	* internal-fn.c (expand_LAUNDER): New function.
c-family/
	* c-common.h (enum rid): Add RID_BUILTIN_LAUNDER.
	* c-common.c (c_common_reswords): Add __builtin_launder.
cp/
	* cp-tree.h (finish_builtin_launder): Declare.
	* parser.c (cp_parser_postfix_expression): Handle RID_BUILTIN_LAUNDER.
	* semantics.c (finish_builtin_launder): New function.
	* pt.c (tsubst_copy_and_build): Handle instantiation of IFN_LAUNDER.
	* constexpr.c (cxx_eval_internal_function): Handle IFN_LAUNDER.
	(potential_constant_expression_1): Likewise.
testsuite/
	* g++.dg/cpp1z/launder1.C: New test.
	* g++.dg/cpp1z/launder2.C: New test.

From-SVN: r241506