Depend on gnureadline when building binary wheel or setupext.check_for_readline() fails

This is a follow up to 4d9f6f00a4f0798e41700c22a839eddff0881692 based on
the discussion in pull request  #7047 where we seem to have found a middle
ground that should make everyone happy :-)

setup.py

@@ -289,7 +289,7 b' install_requires = []'
 
 # add readline
 if sys.platform == 'darwin':
-    if not setupext.check_for_readline():
+    if 'bdist_wheel' in sys.argv[1:] or not setupext.check_for_readline():
         install_requires.append('gnureadline')
 elif sys.platform.startswith('win'):
     extras_require['terminal'].append('pyreadline>=2.0')