Create an aapcs aliased function with mangled names

Currently the function with the aapcs name and ABI is only available
when using unmangled names.  Add an implementation so it is always
available.

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]