KWSys 2020-04-06 (af1f389c)

Code extracted from:

    https://gitlab.kitware.com/utils/kwsys.git

at commit af1f389ca9709a78fdf0103cc20175533054a3e7 (master).

Upstream Shortlog
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Brad King (4):
      313b2f7a SystemTools: Make SystemToolsStatic singleton private to implementation file
      019afb6e SystemTools: Drop GetCurrentWorkingDirectory 'collapse' argument
      c35a377f SystemTools: Refactor CollapseFullPath to call getcwd only when needed
      e3989b18 SystemTools: Restore GetCurrentWorkingDirectory slash conversion on Windows