conftimestamp is not defined in build-all script

When running ./build-all from a fresh clone I see the following error:

configure: Started: ./cmake_helper
Exception in thread phase_0:
Traceback (most recent call last):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "./build-all", line 956, in run
    self.exit_status = self.action( self.path )
  File "./build-all", line 994, in _build
    and builder.configure( )
  File "./build-all", line 432, in configure
    and ( os.path.exists( conftimestamp) )
NameError: name 'conftimestamp' is not defined