bpo-36763: Cleanup precmdline in _PyCoreConfig_Read() by vstinner · Pull Request #13371 · python/cpython

precmdline is only needed in _PyCoreConfig_Read(), not in
config_read_cmdline().

* Reorganize _PyCoreConfig_Read()
* _PyOS_GetOpt() now takes a list of constant strings
* precmdline_parse_cmdline(): mark argv as constant

@vstinner