Rebuild Metal glue when headers change

build.rs

@@ -6,7 +6,7 @@ fn main() {
     }
 
     let metal = Path::new("native/metal/ds4_metal.m");
-    println!("cargo:rerun-if-changed={}", metal.display());
+    println!("cargo:rerun-if-changed=native/metal");
     cc::Build::new()
         .include("native/metal")
         .file(metal)