%current-system and --system

[Greg Hogan]

Hi Guix,

>From my x86_64 machine I am executing offload builds targeting an
aarch64 machine:

$ guix build --system=aarch64-linux --manifest=manifest.scm

Several packages do not build for aarch64 and need to be filtered out.
%current-target-system is #f as these are offload builds not cross
compilation, and %current-system is reported as "x86_64-linux". How
can I access the current "build system"?

If it helps, the manifest is defined at
https://github.com/greghogan/guix-manifest

Thanks,
Greg