Add tooling for josh syncs

Create a crate that handles pulling from and pushing to rust-lang/rust.
This can be invoked with the following:

    $ cargo run -p josh-sync -- rustc-pull
    $ RUSTC_GIT=/path/to/rust/checkout cargo run -p josh-sync -- rustc-push <username>

Author: tgross35

Cargo.toml

@@ -3,6 +3,7 @@ resolver = "2"
 members = [
     "builtins-test",
     "compiler-builtins",
+    "crates/josh-sync",
     "crates/libm-macros",
     "crates/musl-math-sys",
     "crates/panic-handler",

crates/josh-sync/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "josh-sync"
+edition = "2024"
+publish = false
+
+[dependencies]
+directories = "6.0.0"

crates/josh-sync/src/main.rs

@@ -0,0 +1,45 @@
+use std::io::{Read, Write};
+use std::process::exit;
+use std::{env, io};
+
+use crate::sync::{GitSync, Josh};
+
+mod sync;
+
+const USAGE: &str = r#"Utility for synchroniing compiler-builtins with rust-lang/rust
+
+Usage:
+
+    josh-sync rustc-pull
+
+        Pull from rust-lang/rust to compiler-builtins. Creates a commit
+        updating the version file, followed by a merge commit.
+
+    josh-sync rustc-push GITHUB_USERNAME [BRANCH]
+
+        Create a branch off of rust-lang/rust updating compiler-builtins.
+"#;
+
+fn main() {
+    let sync = GitSync::from_current_dir();
+
+    // Collect args, then recollect as str refs so we can match on them
+    let args: Vec<_> = env::args().collect();
+    let args: Vec<&str> = args.iter().map(String::as_str).collect();
+
+    match args.as_slice()[1..] {
+        ["rustc-pull"] => sync.rustc_pull(None),
+        ["rustc-push", github_user, branch] => sync.rustc_push(github_user, Some(branch)),
+        ["rustc-push", github_user] => sync.rustc_push(github_user, None),
+        ["start-josh"] => {
+            let _josh = Josh::start();
+            println!("press enter to stop");
+            io::stdout().flush().unwrap();
+            let _ = io::stdin().read(&mut [0u8]).unwrap();
+        }
+        _ => {
+            println!("{USAGE}");
+            exit(1);
+        }
+    }
+}