Rollup merge of #108404 - ozkanonur:108004, r=jyn514

support `x fmt` for sub and outside of rust directories

This PR makes `x fmt` to be succesfully work from sub or outside dir of rust.

The following cases are tested and the results were successful.
```sh
# from rust/library directory
../x fmt compiler --check
../x fmt compiler/rustc

# from outside of rust directory
../../rust/x fmt library/std library/core --check
../../rust/x fmt library/std
```

Resolves #108004

r? ``@albertlarsan68``

Author: matthiaskrgr