cc3200: Add struct weak link for ustruct.

cc3200/mpconfigport.h

@@ -122,6 +122,7 @@ extern const struct _mp_obj_module_t mp_module_ussl;
     { MP_OBJ_NEW_QSTR(MP_QSTR_ussl),        (mp_obj_t)&mp_module_ussl },      \
 
 #define MICROPY_PORT_BUILTIN_MODULE_WEAK_LINKS \
+    { MP_OBJ_NEW_QSTR(MP_QSTR_struct),      (mp_obj_t)&mp_module_ustruct },   \
     { MP_OBJ_NEW_QSTR(MP_QSTR_re),          (mp_obj_t)&mp_module_ure },       \
     { MP_OBJ_NEW_QSTR(MP_QSTR_json),        (mp_obj_t)&mp_module_ujson },     \
     { MP_OBJ_NEW_QSTR(MP_QSTR_heapq),       (mp_obj_t)&mp_module_uheapq },    \

cc3200/qstrdefsport.h

@@ -70,6 +70,7 @@ Q(/sd/lib)
 #endif
 
 // for module weak links
+Q(struct)
 Q(binascii)
 Q(re)
 Q(json)