re PR c++/89652 (ICE during constexpr evaluation)

re PR c++/89652 (ICE during constexpr evaluation)

	PR c++/89652
	* constexpr.c (struct constexpr_ctx): Change save_exprs type from
	hash_set<tree> to vec<tree>.
	(cxx_eval_call_expression): Adjust for save_exprs being a vec instead
	of hash_set.
	(cxx_eval_loop_expr): Likewise.  Truncate the vector after each
	removal of SAVE_EXPRs from values.
	(cxx_eval_constant_expression) <case SAVE_EXPR>: Call safe_push
	method on save_exprs instead of add.

	* g++.dg/cpp1y/constexpr-89652.C: New test.

From-SVN: r269671