def XcodeArchsVariableMapping(archs, archs_including_64_bit=None):
  """Constructs a dictionary with expansion for $(ARCHS_STANDARD) variable,
  and optionally for $(ARCHS_STANDARD_INCLUDING_64_BIT)."""
  mapping = {'$(ARCHS_STANDARD)': archs}
  if archs_including_64_bit:
    mapping['$(ARCHS_STANDARD_INCLUDING_64_BIT)'] = archs_including_64_bit
  return mapping