py: Add m_malloc_fail function to handle memory allocation error.

A malloc/realloc fail now throws MemoryError.

py/objexcept.c

@@ -17,6 +17,9 @@ typedef struct _mp_obj_exception_t {
     mp_obj_tuple_t args;
 } mp_obj_exception_t;
 
+// Instance of MemoryError exception - needed by mp_malloc_fail
+const mp_obj_exception_t mp_const_MemoryError_obj = {{&mp_type_MemoryError}, MP_OBJ_NULL, {{&mp_type_tuple}, 0}};
+
 // Instance of GeneratorExit exception - needed by generator.close()
 // This would belong to objgenerator.c, but to keep mp_obj_exception_t
 // definition module-private so far, have it here.