qemu: pick pkgs/buildPackages depending on cpu emulation

Fixes Github issue #371.

Author: astro

lib/runner.nix

@@ -31,7 +31,7 @@ let
     then
       # When cross-compiling for a target host, select packages for
       # the target:
-      pkgs.hostPackages
+      pkgs
     else
       # When cross-compiling for CPU emulation in qemu, select
       # packages for the host:

lib/runners/qemu.nix

@@ -40,7 +40,7 @@ let
     if microvmConfig.cpu == null
     then
       # When cross-compiling for a target host, select qemu for the target:
-      pkgs.hostPackages.qemu_kvm
+      pkgs.qemu_kvm
     else
       # When cross-compiling for CPU emulation, select qemu for the host:
       pkgs.buildPackages.qemu;