lib/config: Support symlinked root (fixes #4542, fixes #4353)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4545
LGTM: imsodin, calmh
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f