`EACCES` when checking `islink` for symbolic link on Windows

[topolarity]

On Windows, when attempting to access CLAUDE.md on master:

julia> islink("CLAUDE.md")
ERROR: IOError: stat("CLAUDE.md"): permission denied (EACCES)

It looks like Windows 10+ supports a form of symbolic links, which Git will use now - unfortunately islink and isfile are unhappy about them.

This causes make check-whitespace to fail on Windows for me.