./miri rustc-push suggests the flag --rustc-git but that flag isn't recognized

[saethlin]

╭ ➜ ben@archlinux:~/miri
╰ ➤ ./miri rustc-push saethlin miri
This will pull a copy of the rust-lang/rust history into this Miri checkout, growing it by about 1GB.
To avoid that, abort now and set the `--rustc-git` flag to an existing rustc checkout. Proceed? [y/N] N
╭ ➜ ben@archlinux:~/miri
╰ ➤ ./miri rustc-push saethlin miri --rustc-git=/home/ben/rust
Error: Too many arguments for `./miri rustc-push GITHUB_USER BRANCH`
╭ ➜ ben@archlinux:~/miri
╰ ➤ ./miri --rustc-git=/home/ben/rust rustc-push saethlin miri
Unknown or missing command. Usage:
<snip>

This flag sounds useful, maybe we just need to fix some parsing?