Cleanup after some refactoring in rustc_target

Author: Urgau

src/driver/aot.rs

@@ -304,8 +304,12 @@ pub(crate) fn run_aot(
     };
 
     // FIXME handle `-Ctarget-cpu=native`
-    let target_cpu =
-        tcx.sess.opts.cg.target_cpu.as_ref().unwrap_or(&tcx.sess.target.cpu).to_owned();
+    let target_cpu = match tcx.sess.opts.cg.target_cpu {
+        Some(ref name) => name,
+        None => tcx.sess.target.cpu.as_ref(),
+    }
+    .to_owned();
+
     Box::new((
         CodegenResults {
             modules,