re PR c++/49528 (g++ fails to destroy temporary object when subobject is used to initialize a reference)

	PR c++/49528
	* semantics.c (potential_constant_expression_1): A TARGET_EXPR
	with a cleanup isn't constant.
	(cxx_eval_constant_expression): Likewise.
	* init.c (expand_default_init): Use maybe_constant_init.

From-SVN: r175409