GPU backend

Adds GPU backend and "CUDA" feature to all the tests. As of MR creation, there were no forks in tested IRs so only vanilla non-parallel (single block, single thread) codegen has been tested.

hercules_rt/build.rs

@@ -11,8 +11,8 @@ fn main() {
             .status()
             .expect("PANIC: NVCC failed when building runtime. Is NVCC installed?");
         Command::new("ar")
-            .args(&["crus", "librtdefs.a", "rtdefs.o"])
             .current_dir(&Path::new(&out_dir))
+            .args(&["crus", "librtdefs.a", "rtdefs.o"])
             .status()
             .unwrap();