Refactor copying decl section names

gcc/

	* cgraph.h (symtab_node::get_section): Constify.
	(symtab_node::set_section): Declare new overload.
	* symtab.c (symtab_node::set_section): Define new overload.
	(symtab_node::copy_visibility_from): Use new overload of
	symtab_node::set_section.
	(symtab_node::resolve_alias): Same.
	* tree.h (set_decl_section_name): Declare new overload.
	* tree.c (set_decl_section_name): Define new overload.
	* tree-emutls.c (get_emutls_init_templ_addr): Same.
	* cgraphclones.c (cgraph_node::create_virtual_clone): Use new
	overload of symtab_node::set_section.
	(cgraph_node::create_version_clone_with_body): Same.
	* trans-mem.c (ipa_tm_create_version): Same.

gcc/c
	* c-decl.c (merge_decls): Use new overload of
	set_decl_section_name.

gcc/cp
	* decl.c (duplicate_decls): Use new overload of
	set_decl_section_name.
	* method.c (use_thunk): Same.
	* optimize.c (maybe_clone_body): Same.
	* coroutines.cc (act_des_fn): Same.

gcc/d
	* decl.cc (finish_thunk): Use new overload of
	set_decl_section_name