Diagnose certain constraint errors as hard errors, but otherwise treat them the same as normal SFINAE-type errors.

2019-11-27  Andrew Sutton  <asutton@lock3software.com>

	Diagnose certain constraint errors as hard errors, but otherwise treat
	them the same as normal SFINAE-type errors. Also, generally clean up
	the satisfaction functions.

gcc/cp/
	* constexpr.c (cxx_eval_constant_expression): Use
	evaluate_concept_check.
	* constraint.cc (normalize_concept_definition): Accept a diagnostic
	flag and only cache when not diagnosing errors.
	(decl_satisfied_cache): Map to trees instead of bools.
	(satisfy_atom): Guarantee a location for the errors, propagate complain
	flags to force_rvalue, and emit errors for non-boolean constraints.
	(get_normalized_constraints_and_args): New overloads. Factored out of
	satisfy_constraint_expression and satisfy_declaration_constraints.
	(satisfy_constraint_expression): Propagate diagnostic info to
	normalization.
	(satisfy_declaration_constraints): New. Factored out of
	constraints_satisfied_p.
	(constraint_satisfaction_value): New. Calls
	satisfy_constraint_expression or satisfy_declaration_constraints.
	(constraints_satisfied_p): Call constraint_satisfaction_value.
	(evaluate_concept_check): Don't take tsubst_falgs_t. Replay
	satisfaction if an error is encountered.
	(current_failed_constraint): Moved from pt.c.
	(diagnose_constraints): Call constraint_satisfaction_value.
	* cp-tree.h: Update declarations.
	* pt.c (current_failed_constraint): Moved to constraint.cc.
	* semantics.c (finish_id_expression_1): Remove a duplicate case.

gcc/testsuite/
	* g++.dg/concepts/pr84330.C: Update diagnostics.
	* g++.dg/cpp2a/concepts-requires2.C: Likewise.

From-SVN: r278768