chore: add nix-shell stuff

sys/Cargo.toml

@@ -22,7 +22,7 @@ libc = "0.2"
 num_cpus   = "1.11"
 cc         = "1.0"
 pkg-config = "0.3"
-bindgen    = "0.54"
+bindgen    = "0.55"
 
 [target.'cfg(target_env = "msvc")'.build-dependencies]
 vcpkg = "0.2"

sys/shell.nix

@@ -0,0 +1,21 @@
+let
+  mozilla = import (builtins.fetchTarball https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz);
+in
+
+with (import <nixpkgs> {
+  overlays = [mozilla];
+});
+
+mkShell {
+  name = "ffmpeg-sys";
+
+  buildInputs = [
+    # For building.
+    clang rustChannels.stable.rust pkg-config ffmpeg
+  ];
+
+  RUST_BACKTRACE = 1;
+  RUSTFLAGS = "-C target-cpu=native";
+
+  LIBCLANG_PATH = "${llvmPackages.libclang}/lib";
+}