re PR c++/88395 (ICE: Segmentation fault signal terminated program cc1plus, with -std=c++2a -fconcepts)

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

	PR c++/88395
	Prevent recursive satisfaction by adding requests to the instantiation
	stack.

gcc/cp/
	* constraint.cc (satisfy_declaration_constraints): Push tinst levels
	around satisfaction.

gcc/testsuite/
	* g++.dg/cpp2a/concepts-pr88395.C: New.
	* g++.dg/cpp2a/concepts-recursive-sat1.C: New.
	* g++.dg/cpp2a/concepts-recursive-sat2.C: New.
	* g++.dg/cpp2a/concepts-recursive-sat3.C: New.

From-SVN: r278773