Add multithreading to rust code.

rust/usr/testbed/src/main.rs

@@ -9,6 +9,7 @@ use mammoth::debug;
 use mammoth::define_entry;
 use mammoth::syscall::debug;
 use mammoth::syscall::z_err_t;
+use mammoth::thread;
 use yellowstone::GetEndpointRequest;
 use yellowstone::YellowstoneClient;
 
@@ -41,5 +42,12 @@ pub extern "C" fn main() -> z_err_t {
 
     debug!("Got endpoint w/ cap: {:#x}", endpoint.endpoint);
 
+    let e: thread::ThreadEntry = |_| {
+        debug!("Testing 1 2 3");
+    };
+    let t = thread::Thread::spawn(&e, core::ptr::null());
+
+    t.join().expect("Failed to wait.");
+
     0
 }