Improve GC finalisation code; add option to disable it.
diff --git a/unix/mpconfigport.h b/unix/mpconfigport.h
index 254d14d..b8ee020 100644
--- a/unix/mpconfigport.h
+++ b/unix/mpconfigport.h
@@ -4,6 +4,7 @@
 #define MICROPY_EMIT_THUMB          (0)
 #define MICROPY_EMIT_INLINE_THUMB   (0)
 #define MICROPY_ENABLE_GC           (1)
+#define MICROPY_ENABLE_FINALISER    (1)
 #define MICROPY_MEM_STATS           (1)
 #define MICROPY_DEBUG_PRINTERS      (1)
 #define MICROPY_ENABLE_REPL_HELPERS (1)