pythongh-119253: use ImportError in _ios_support (python#119254)

Lib/_ios_support.py

@@ -5,15 +5,15 @@
     # ctypes is an optional module. If it's not present, we're limited in what
     # we can tell about the system, but we don't want to prevent the module
     # from working.
-    print("ctypes isn't available; iOS system calls will not be available")
+    print("ctypes isn't available; iOS system calls will not be available", file=sys.stderr)
     objc = None
 else:
     # ctypes is available. Load the ObjC library, and wrap the objc_getClass,
     # sel_registerName methods
     lib = util.find_library("objc")
     if lib is None:
         # Failed to load the objc library
-        raise RuntimeError("ObjC runtime library couldn't be loaded")
+        raise ImportError("ObjC runtime library couldn't be loaded")
 
     objc = cdll.LoadLibrary(lib)
     objc.objc_getClass.restype = c_void_p