re PR objc/24867 (many N^2 loops in objc frontend)

re PR objc/24867 (many N^2 loops in objc frontend)

	PR objc/24867
	* objc-act.c (build_sized_array_type): New function.
	(add_objc_string): Use it.
	(generate_protocol_list): Likewise.
	(generate_objc_image_info): Likewise.
	(add_field_decl): New function.
	(objc_build_struct): Use a VEC rather than building a TREE_LIST.
	(generate_struct_by_value_array): Use add_field_decl.
	(build_objc_symtab_template): Likewise.
	(build_module_descriptor): Likewise.
	(build_objc_exception_stuff): Likewise.
	(build_protocol_template): Likewise.
	(build_method_prototype_list_template): Likewise.
	(build_method_prototype_template): Likewise.
	(build_category_template): Likewise.
	(build_selector_template): Likewise.
	(build_class_template): Likewise.
	(build_super_template): Likewise.
	(build_ivar_template): Likewise.
	(build_ivar_list_template): Likewise.
	(build_method_list_template): Likewise.
	(build_method_template): Likewise.

From-SVN: r161777