This makes a number of changes to improve compatibility with the
"nogil" Python fork as well as the upcoming 3.11 release.

 - Fix _code_reduce for 3.11b0 and nogil Python

 - Use instr.argval in _walk_global_ops. This avoids adding a special
   case for 3.11+ (and is useful for nogil Python). In 3.11+, the argval
   for LOAD_GLOBAL would need to be divided by two to access the correct
   name. The 'argval' field already stores the correct name.

 - Set '__builtins__' before constructing de-pickled functions. (Useful
   for nogil Python)

 - Fix test_recursion_during_pickling in Python 3.11+. Objects now have
   a default `__getstate__` method so `__getattr__` was never called,
   but `__getattribute__` would still be called.