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-bdwgc-sys/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "nix-bindings-bdwgc-sys"
+version = "0.2.0"
+edition = "2021"
+build = "build.rs"
+license = "LGPL-2.1"
+
+[lib]
+path = "src/lib.rs"
+
+[dependencies]
+
+[build-dependencies]
+bindgen = "0.69"
+pkg-config = "0.3"

nix-bindings-bdwgc-sys/README.md

@@ -0,0 +1,4 @@
+# nix-bindings-bdwgc-sys
+
+This crate contains generated bindings for the Boehm-Demers-Weiser garbage collector (`bdw-gc`).
+**You should not have to use this crate directly,** and so you should probably not add it to your dependencies.

nix-bindings-bdwgc-sys/build.rs

@@ -0,0 +1,27 @@
+use std::env;
+use std::path::PathBuf;
+
+fn main() {
+    println!("cargo:rerun-if-changed=include/bdwgc.h");
+
+    let mut args = Vec::new();
+    for path in pkg_config::probe_library("bdw-gc")
+        .unwrap()
+        .include_paths
+        .iter()
+    {
+        args.push(format!("-I{}", path.to_str().unwrap()));
+    }
+
+    let bindings = bindgen::Builder::default()
+        .header("include/bdwgc.h")
+        .clang_args(args)
+        .parse_callbacks(Box::new(bindgen::CargoCallbacks::new()))
+        .generate()
+        .expect("Unable to generate bindings");
+
+    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
+    bindings
+        .write_to_file(out_path.join("bindings.rs"))
+        .expect("Couldn't write bindings!");
+}

nix-bindings-bdwgc-sys/include/bdwgc.h

@@ -0,0 +1,2 @@
+#define GC_THREADS
+#include <gc/gc.h>

nix-bindings-bdwgc-sys/src/lib.rs

@@ -0,0 +1,7 @@
+#![allow(non_upper_case_globals)]
+#![allow(non_camel_case_types)]
+#![allow(non_snake_case)]
+#![allow(dead_code)]
+#![allow(clippy::all)]
+
+include!(concat!(env!("OUT_DIR"), "/bindings.rs"));