In commit 7f89053953 (cmSystemTools: Return KWSys Status from CreateLink
and CreateSymlink, 2021-04-15) we just took the `-err` from libuv and
treated it as a POSIX error. This is accurate on POSIX, but on Windows
does not match the POSIX error codes.
Use `uv_fs_get_system_error` to get the actual system error code.
This requires libuv 1.38 or higher. Require that for Windows, but
fall back to the previous approach on POSIX.
The allows `-E create_symlink` to work on Windows. It utilizes
`uv_fs_symlink`. I am still unsure exactly which Windows platforms will
work without requiring Administrator privileges or needing a user/group
with the "Create Symbolic Links" User Rights. It does work with my
Windows 10 Pro with Developer Mode turned on. In the test suite check
that the symlink either worked or failed with a permissions error.
Use recent changes in cmSystemTools::FileExists to check that a symlink
is broken.
The logic added by commit ffc0b5e4 (Overwrite the symlink if it already
exists, 2007-02-15) does not recognize and remove existing broken links
before replacing them. Improve the logic to remove any existing
destination file or link (but not directory). On failure, report an
error message explaining why the existing path could not be removed or
the new one could not be created.
Add a RunCMake.CommandLine test to cover 'cmake -E' cases. Start with
test cases covering 'cmake -E create_symlink' behavior on UNIX platforms.
Brad King