ignore EEXIST errors when creating symlinks for output standalone (#40150)
I think the `EEXIST` error may be because next already copies some files here
https://github.com/vercel/next.js/blob/e91cbcc03d7226cc6f2edb66c656ae08bdf5b903/packages/next/build/index.ts#L2442
partially fixes #36386 when using pnpm linker
## Bug
- [x] Related issues linked using
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`