Hello world in AAarch64 Debian Buster

[Cecil Ward]

I have a raspberry pi 3B+ running raspbian stretch 32-bit with a 
containerised guest o/s inside it using systemd-nspawn, the guest 
o/s being AAarch64 Debian Buster.

Inside AAarch64 Debian Buster, I run the following from the shell 
and get an error from the gdc compiler:

root at debian-buster-64:~#  gdc -O3 -frelease -S test.d
cc1d: error: cannot find source code for runtime library file 
'object.d'
cc1d: note: dmd might not be correctly installed. Run 'dmd -man' 
for installation instructions.

(null):0: confused by earlier errors, bailing out
root at debian-buster-64:~#

Any clues as to where I should head from here?