Deno compile - Warning for dangling symlink in embedded files

[dsherret]

There's probably not much reason for someone to include a symlink in the vfs that doesn't point to a valid file system entry in the embedded executable. We should probably warn in this case.

I'm not sure we should always include the file because it might be something the user doesn't want to include or they might also be forgetting to include other files. The warning should help them make the right choice or ignore.