fix build

build.rs

@@ -0,0 +1,21 @@
+fn main() {
+    cxx_build::bridge("src/bindings/mod.rs")
+        .file("src/bindings/nix.cpp")
+        .flag("-std=c++2a")
+        .flag("-O2")
+        .flag("-include")
+        .flag("nix/config.h")
+        .flag("-I")
+        .flag(concat!(env!("NIX_INCLUDE_PATH"), "/nix"))
+        .compile("nixbinding");
+    println!("cargo:rerun-if-changed=src/bindings");
+
+    pkg_config::Config::new()
+        .atleast_version("2.4")
+        .probe("nix-store")
+        .unwrap();
+    pkg_config::Config::new()
+        .atleast_version("2.4")
+        .probe("nix-main")
+        .unwrap();
+}