PR c++/49172
	* decl.c (cp_finish_decl): Adjust init_const_expr_p for refs.
	(grokdeclarator): constexpr doesn't apply const for refs.
	* parser.c (cp_parser_initializer_clause): Don't call
	maybe_constant_value here.
	* call.c (initialize_reference): Handle constexpr.

From-SVN: r175284