The Linux headers on arm64 architectures contain references to common
arch/arm/ headers which were not bundled by the SDK so far.
Check if we're packing the SDK for an arm64 target and if we do, also
include arch/arm headers as well.
Fixes FS#1725.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit 4bb8a678e0)