muon-meson cannot cross build itself. Even upstream uses Python meson
for cross building muon-meson. I suggest doing the same in Debian until
muon-meson gains this capability. Fundamentally, it would need a way to
communicate a build architecture compiler, but presently it understands
neither CC_FOR_BUILD nor --native-file. Please consider applying the
attached patch as a stop-gap solution to be reverted once muon-meson
advances.

Helmut