Fix handling of broken symlinks in filelib

This fixes a bug introduced in f11aabdc9fec593c31e6c4f3fa25c1707e9c35df where filelib:eval_read_file_info/2 was made to use file:read_link_info/1 to never follow symlinks. This fixed wildcard/1 but broke every other function using eval_read_file_info/2.

@lpgauth
@stolen
Okay, but doesn't `{win32,_} = os:type()` make it fail on non-Windows platforms in a misleading way? So, how about improving that in `symlinks/1` and `ensure_dir_symlink/1`, while you're at it?