Add ABI tagging to crates, adjust rustc output and runtime stack-frame setup so access to argv works.

src/rt/rust_task.h

@@ -56,6 +56,7 @@ rust_task : public maybe_proxy<rust_task>,
     ~rust_task();
 
     void start(uintptr_t exit_task_glue,
+               uintptr_t spawnee_abi,
                uintptr_t spawnee_fn,
                uintptr_t args,
                size_t callsz);