Never long live the main dictionary.

It's contents change often and may be referenced elsewhere.

Fixes adafruit#1443

Author: tannewt

py/gc_long_lived.c

@@ -27,6 +27,7 @@
 #include "py/emitglue.h"
 #include "py/gc_long_lived.h"
 #include "py/gc.h"
+#include "py/mpstate.h"
 
 mp_obj_fun_bc_t *make_fun_bc_long_lived(mp_obj_fun_bc_t *fun_bc, uint8_t max_depth) {
     #ifndef MICROPY_ENABLE_GC
@@ -88,7 +89,7 @@ mp_obj_dict_t *make_dict_long_lived(mp_obj_dict_t *dict, uint8_t max_depth) {
     #ifndef MICROPY_ENABLE_GC
     return dict;
     #endif
-    if (dict == NULL || max_depth == 0) {
+    if (dict == NULL || max_depth == 0 || dict == &MP_STATE_VM(dict_main)) {
         return dict;
     }
     // Don't recurse unnecessarily. Return immediately if we've already seen this dict.