Rerun the build script if the bin/{}.a archive has changed

riscv-rt/build.rs

@@ -14,15 +14,10 @@ fn main() {
     if target.starts_with("riscv") {
         let mut target = Target::from_target_str(&target);
         target.retain_extensions("imfdc");
+        let archive = format!("bin/{}.a", target.to_string());
 
-        let target = target.to_string();
-
-        fs::copy(
-            format!("bin/{}.a", target),
-            out_dir.join(format!("lib{}.a", name)),
-        )
-        .unwrap();
-
+        fs::copy(&archive, out_dir.join(format!("lib{}.a", name))).unwrap();
+        println!("cargo:rerun-if-changed={}", archive);
         println!("cargo:rustc-link-lib=static={}", name);
     }