[syslinux] efi64: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]

[Joakim Tjernlund]

When building for efi64 there are a ton of
  warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
Feels a bit unsafe, are those harmless?

 Jocke