Merge #15335: Fix lack of warning of unrecognized section names

1a7ba84e11 Fix lack of warning of unrecognized section names (Akio Nakamura)

Pull request description:

  In #14708, It was introduced that to warn when unrecognized section names are exist in the config file.
  But ```m_config_sections.clear()```  in ```ArgsManager::ReadConfigStream()``` is called every time when reading each configuration file, so it can warn about only last reading file if ```includeconf``` exists.

  This PR fix lack of warning by collecting all section names by moving ```m_config_sections.clear()```  to ```ArgsManager::ReadConfigFiles()``` .
  Also add a test code to confirm this situation.

Tree-SHA512: 26aa0cbe3e4ae2e58cbe73d4492ee5cf465fd4c3e5df2c8ca7e282b627df9e637267af1e3816386b1dc6db2398b31936925ce0e432219fec3a9b3398f01e3e65

0 files changed, 0 insertions, 0 deletions