On macos arm64, objc.objc_msgSend seg-faults when called from ipython

Related to #561 , ipython/ipykernel/etc will seg-fault when running the following test code (based on appnope):

```
import ctypes
import ctypes.util

objc = ctypes.cdll.LoadLibrary(ctypes.util.find_library('objc'))

def _utf8(s):
"""ensure utf8 bytes"""
if not isinstance(s, bytes):
s = s.encode('utf8')
return s

def n(name):
"""create a selector name (for methods)"""
return objc.sel_registerName(_utf8(name))

def C(classname):
"""get an ObjC Class by name"""
return objc.objc_getClass(_utf8(classname))

NSString = C('NSString')

objc.objc_msgSend(NSString, n("stringWithUTF8String:"), _utf8("reason"))
```

The stack trace on an arm64 mac (DTK) says: `python[97504:4905234] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** +[NSString stringWithUTF8String:]: NULL cString'`

Note that this code will work with both system python (macos 11.0.1) and conda-forge python 3.9.0 for osx-arm64. However, it will seg-fault with ipython/ipykernel from conda-forge _or_ with ipython installed with the system python via pip.