Split monolithic raw crates into sys crates

Creating a crate for bwd-gc highlights the fact that it would be nice to
fix 2!

The file blocklist is a lost less unmaintainable then the more
fine-grained one we had before.

Fix #9

nix-bindings-util-sys/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "nix-bindings-util-sys"
-version = "0.1.1"
+version = "0.2.0"
 edition = "2021"
 build = "build.rs"
 license = "LGPL-2.1"
@@ -10,6 +10,8 @@ repository = "https://github.com/nixops4/nix-bindings-rust"
 [lib]
 path = "src/lib.rs"
 
+[dependencies]
+
 [build-dependencies]
 bindgen = "0.69"
 pkg-config = "0.3"