only ignore arm when there's no ret

Author: jdonszelmann

tests/codegen/naked-fn/aligned.rs

@@ -1,6 +1,6 @@
 //@ compile-flags: -C no-prepopulate-passes -Copt-level=0
 //@ needs-asm-support
-//@ only-x86_64
+//@ ignore-arm no "ret" mnemonic
 
 #![crate_type = "lib"]
 #![feature(naked_functions, fn_align)]