Vendor dependencies

Let's see how I like this workflow.

vendor/iana-time-zone-haiku/build.rs

@@ -0,0 +1,20 @@
+use std::env;
+
+fn main() {
+    cxx_build::bridge("src/lib.rs")
+        .file("src/implementation.cc")
+        .flag_if_supported("-std=c++11")
+        .compile("tz_haiku");
+
+    println!("cargo:rerun-if-changed=src/lib.rs");
+    println!("cargo:rerun-if-changed=src/implementation.cc");
+    println!("cargo:rerun-if-changed=src/interface.h");
+
+    let target = env::var_os("TARGET").expect("cargo should set TARGET env var");
+    let target = target
+        .to_str()
+        .expect("TARGET env var should be valid UTF-8");
+    if target.contains("haiku") {
+        println!("cargo:rustc-link-lib=be");
+    }
+}