Draft: Emulate hard-linking symlinks on macOS hosts

[doanbaotrung]

On macOS hosts, native linkat(2) returns EINVAL when linking a symbolic link directly (i.e. with AT_SYMLINK_NOFOLLOW). Linux allows this unconditionally.

Emulate this by reading the symlink target, converting any absolute target path to a relative path to keep it contained in the sysroot, and creating a new symbolic link at the destination using symlinkat.

Fix #237

---

Summary by cubic

Emulates Linux behavior on macOS for hard-linking a symlink: linkat(..., AT_SYMLINK_NOFOLLOW) now creates a new symlink at the destination with the same target. Absolute targets are rewritten to relative to keep links within the sysroot. Fixes #237.

• New Features

  • Emulate symlink hard-linking on macOS by creating a new symlink when AT_SYMLINK_NOFOLLOW is set (handles EINVAL).
  • Normalize absolute symlink targets to relative in both linkat emulation and symlinkat.

• Refactors

  • Export dirfd_guest_base_path for target normalization.
  • Add debug logging for symlinkat in the syscall dispatcher.

^{Written for commit 12df8f2. Summary will update on new commits.}