c++: DECL_LOCAL_FUNCTION_P -> DECL_LOCAL_DECL_P

Our handling of block-scope extern decls is insufficient for modern
C++, in particular modules, (but also constexprs).  We mark such local
function decls, and this patch extends that to marking local var decls
too, so mainly a macro rename.  Also, we set this flag earlier, rather
than learning about it when pushing the decl.  This is a step towards
handling these properly.

	gcc/cp/
	* cp-tree.h (DECL_LOCAL_FUNCTION_P): Rename to ...
	(DECL_LOCAL_DECL_P): ... here.  Accept both fns and vars.
	* decl.c (start_decl): Set DECL_LOCAL_DECL_P for local externs.
	(omp_declare_variant_finalize_one): Use DECL_LOCAL_DECL_P.
	(local_variable_p): Simplify.
	* name-lookup.c (set_decl_context_in_fn): Assert DECL_LOCAL_DECL_P
	is as expected.  Simplify.
	(do_pushdecl): Don't set decl_context_in_fn for friends.
	(is_local_extern): Simplify.
	* call.c (equal_functions): Use DECL_LOCAL_DECL_P.
	* parser.c (cp_parser_postfix_expression): Likewise.
	(cp_parser_omp_declare_reduction): Likewise.
	* pt.c (check_default_tmpl_args): Likewise.
	(tsubst_expr): Assert nested reduction function is local.
	(type_dependent_expression_p): Use DECL_LOCAL_DECL_P.
	* semantics.c (finish_call_expr): Likewise.
	libcc1/
	* libcp1plugin.cc (plugin_build_call_expr): Use DECL_LOCAL_DECL_P.