Emulate other architectures in owl nodes too

Allows cross-compilation of packages for RISC-V that are known to try to
run RISC-V programs in the host.

Reviewed-by: Aleix Boné <abonerib@bsc.es>

m/module/emulation.nix

@@ -0,0 +1,3 @@
+{
+  boot.binfmt.emulatedSystems = [ "armv7l-linux" "aarch64-linux" "powerpc64le-linux" "riscv64-linux" ];
+}