core: Serialize all access to the environment using a weak global task

src/rt/rust_builtin.cpp

@@ -781,6 +781,12 @@ rust_task_unweaken(rust_port_id chan) {
     task->kernel->unweaken_task(chan);
 }
 
+extern "C" CDECL uintptr_t*
+rust_global_env_chan_ptr() {
+    rust_task *task = rust_get_current_task();
+    return task->kernel->get_global_env_chan();
+}
+
 //
 // Local Variables:
 // mode: C++