Suppress GC stats when obviously not needed

This should help future improvements where these stats can be
bignums that do not fit into intmax_t.
* src/alloc.c (struct gcstat, gcstat): New type and static var,
to package up GC statistics into one C object.  It replaces ...
(total_free_intervals, total_intervals, total_strings)
(total_free_strings, total_string_bytes, total_vectors)
(total_vector_slots, total_free_vector_slots): ... these
removed static vars.  All uses changed.
(garbage_collect_1): Accept a struct gcstat *, not a void *
which was not used anymore anyway.  Return a bool indicating
success, instead of a Lisp object.  All callers changed.
(garbage_collect): New function.  All C callers of
Fgarbage_collect changed to use it, since none of them use the
return value.  Now, only Lisp code uses Fgarbage_collect.
(Fgarbage_collect): No longer noinline.  Cons up the return
value here, not in garbage_collect_1.

lib-src/make-docfile.c

@@ -1107,6 +1107,9 @@ scan_c_stream (FILE *infile)
 		g->flags |= DEFUN_noreturn;
 	      if (strstr (input_buffer, "const"))
 		g->flags |= DEFUN_const;
+
+	      /* Although the noinline attribute is no longer used,
+		 leave its support in, in case it's needed later.  */
 	      if (strstr (input_buffer, "noinline"))
 		g->flags |= DEFUN_noinline;
 	    }