[Lazarus] Aarch64 as CPU target for RPi3 with Linux as OS

[Alfred]

For all RPi's I use Arch Linux.

However, at the moment, no easy Arch aarch64 distro available for RPi3.
URL: https://archlinuxarm.org/platforms/armv8/broadcom/raspberry-pi-3
Therefor, I used the general libraries to build the aarch64 
cross-compiler.
URL: https://archlinuxarm.org/platforms/armv8/generic.

But, we indeed all have to wait for a 64bit kernel.

For real (industrial) applications, i will use the ODroid C2 !
Its better than the RPi3 for my purposes.

However, the main question still stands:

How to setup Lazarus to compile for Aarch64 ??
Fpc does NOT know what to do with -Pa64.
Fpc does know what to do with -Paarch64.