add libbuild_zynq from drtio port

src/libbuild_zynq/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+authors = ["M-Labs"]
+name = "build_zynq"
+version = "0.0.0"
+
+[lib]
+name = "build_zynq"
+path = "lib.rs"

src/libbuild_zynq/lib.rs

@@ -0,0 +1,13 @@
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+pub fn cfg() {
+    // Handle rustc-cfg file
+    let cfg_path = "../../build/rustc-cfg";
+    println!("cargo:rerun-if-changed={}", cfg_path);
+
+    let f = BufReader::new(File::open(cfg_path).unwrap());
+    for line in f.lines() {
+        println!("cargo:rustc-cfg={}", line.unwrap());
+    }
+}