Fix #1563807: _ctypes built on AIX fails with ld ffi error.

The contents of ffi_darwin.c must be compiled unless __APPLE__ is
defined and __ppc__ is not.

Backport from trunk.

Misc/NEWS

@@ -70,6 +70,8 @@ Core and builtins
 Extension Modules
 -----------------
 
+- Bug #1563807: _ctypes built on AIX fails with ld ffi error.
+
 - Bug #1598620: A ctypes Structure cannot contain itself.
  
 - Bug #1588217: don't parse "= " as a soft line break in binascii's

Modules/_ctypes/libffi/src/powerpc/ffi_darwin.c

-#ifdef __ppc__
+#if !(defined(__APPLE__) && !defined(__ppc__))
 /* -----------------------------------------------------------------------
    ffi.c - Copyright (c) 1998 Geoffrey Keating