fix gitignore

kernel/build.rs

@@ -0,0 +1,7 @@
+fn main() {
+    let arch = std::env::var("CARGO_CFG_TARGET_ARCH").unwrap();
+    // Tell cargo to pass the linker script to the linker..
+    println!("cargo:rustc-link-arg=-Tlinker-{arch}.ld");
+    // ..and to re-run if it changes.
+    println!("cargo:rerun-if-changed=linker-{arch}.ld");
+}