Create an aapcs aliased function with mangled names

Currently the function with the aapcs name and ABI is only available
when using unmangled names. Adjust `intrinsics!` to always create this
function so it can be reached regardless of features.

Author: tgross35

compiler-builtins/src/macros.rs

@@ -331,6 +331,12 @@ macro_rules! intrinsics {
             $($body)*
         }
 
+        #[cfg(target_arch = "arm")]
+        $(#[$($attr)*])*
+        pub extern "aapcs" fn $alias( $($argname: $ty),* ) $(-> $ret)? {
+            $name($($argname),*)
+        }
+
         #[cfg(all(target_arch = "arm", not(feature = "mangled-names")))]
         mod $name {
             #[no_mangle]