Rollup merge of #108021 - zephaniahong:oldx, r=albertlarsan68

make x look for x.py if shell script does not exist

Fixes #107907

Manually tested by doing the following after changes were made:
1. `cargo install --path src/tools/x`
2. checked out old version:  commit hash `775c3c0` from rust-lang/rust#99992
3. Ran `x --help` and it works. Previously, it was giving the error `x.py not found`

Author: matthiaskrgr