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.

juno_samples/antideps/Cargo.toml

@@ -9,10 +9,10 @@ name = "juno_antideps"
 path = "src/main.rs"
 
 [build-dependencies]
-juno_build = { path = "../../juno_build" }
+juno_build = { path = "../../juno_build", features = [] }
 
 [dependencies]
-juno_build = { path = "../../juno_build" }
-hercules_rt = { path = "../../hercules_rt" }
+juno_build = { path = "../../juno_build", features = [] }
+hercules_rt = { path = "../../hercules_rt", features = [] }
 with_builtin_macros = "0.1.0"
 async-std = "*"