Add rust to go dynamic library example.

rust-to-go-dynamic/build.rs

@@ -0,0 +1,13 @@
+use std::process::Command;
+
+fn main() {
+    println!(r"cargo:rustc-link-search=target/debug");
+    let os = Command::new("uname")
+        .output().unwrap();
+    let ext = match String::from_utf8_lossy(os.stdout.as_slice()).into_owned().trim_end().as_ref() {
+        "Darwin" => "dylib",
+        _ => "so"
+    };
+    Command::new("go").args(&["build", "-o", &format!("target/debug/libdouble_input.{}", ext), "-buildmode=c-shared", "src/double.go"])
+        .status().unwrap();
+}