Add codegen option for branch protection and pointer authentication on AArch64

The branch-protection codegen option enables the use of hint-space pointer
authentication code for AArch64 targets

compiler/rustc_codegen_llvm/src/declare.rs

@@ -45,8 +45,13 @@ fn declare_raw_fn(
         llvm::Attribute::NoRedZone.apply_llfn(Function, llfn);
     }
 
+    if cx.tcx.sess.target.arch == "aarch64" {
+        attributes::set_branch_protection(cx.tcx.sess, llfn);
+    }
+
     attributes::default_optimisation_attrs(cx.tcx.sess, llfn);
     attributes::non_lazy_bind(cx.sess(), llfn);
+
     llfn
 }