[build] first pass at multiarch support

Changing bonnibel to respect the --arch flag to configure. This requires
some reworking of modules, mostly in the addition of the ModuleList
class instead of just a dict of modules.

qemu.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 
 root=$(dirname $0)
-build="${root}/build"
+build="${root}/build.amd64"
 assets="${root}/assets"
 
 no_build=""