On Windows untracked files from a previous builds are not cleaned up if the path length is too long

Summary

On Windows untracked files from a previous builds are not cleaned up if the path length is too long

Steps to reproduce

Run a build job that creates a long path. Use anything that uses \\? paths or has opted into the new long path support on newer Windows 10 builds to create some long paths. Something like:

job:
  script:
    - cmake -E touch short_path
    - cmake -E make_directory loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooonnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnggggggggggggggggggggggggggggggggggggggggggggggggggggg_path
    - cmake -E touch 
loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooonnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnggggggggggggggggggggggggggggggggggggggggggggggggggggg_path/file

Actual behavior

The next build to run fails to remove the long paths. Not only that, but it ignores the failures and tries to run the build script:

...
Removing short_path
warning: Could not stat path 'loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooonnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnggggggggggggggggggggggggggggggggggggggggggggggggggggg_path': Filename too long
warning: Could not stat path 'loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooonnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnggggggggggggggggggggggggggggggggggggggggggggggggggggg_path/file': Filename too long
HEAD is now at 49e89488 ...
From http://gitlab/xx/xxx
Checking out 49e89488 as branch_name...
Skipping Git submodules setup
$ cmake -E touch short_path
...

Expected behavior

GitLab Runner should be able to delete long paths by both:

• Using \\? prefixed paths
• Opting in to the new long path support in Windows 10

See: https://docs.microsoft.com/en-us/windows/desktop/FileIO/naming-a-file

Environment description

Are you using shared Runners on GitLab.com? Or is it a custom installation?

Custom installation

Which executors are used? Please also provide the versions of related tools

Shell executor on Windows 10 version 1703

Used GitLab Runner version

10.5.0