Use LLVM features for arm64e_apple_ios target

We need to use LLVM features here. Otherwise we get warnings such as
'+paca' is not a recognized feature for this target (ignoring feature)

compiler/rustc_target/src/spec/targets/arm64e_apple_ios.rs

@@ -16,7 +16,7 @@ pub fn target() -> Target {
         data_layout: "e-m:o-i64:64-i128:128-n32:64-S128".into(),
         arch: arch.target_arch(),
         options: TargetOptions {
-            features: "+neon,+fp-armv8,+apple-a12,+v8.3a,+paca,+pacg".into(),
+            features: "+neon,+fp-armv8,+apple-a12,+v8.3a,+pauth".into(),
             max_atomic_width: Some(128),
             frame_pointer: FramePointer::NonLeaf,
             ..base