bxx: Added automatic run of codegen.
bxx: Added automatic run of codegen.

Prior to this change the BXX codegen had to be run manually in case
changes to templates/mappings where made. It now runs the codegen
whenever changes to the generator, templates or codegen/*.json files.

madsbk/bohrium,bh107/bohrium,madsbk/bohrium,bh107/bohrium,madsbk/bohrium,bh107/bohrium,bh107/bohrium,madsbk/bohrium