lib: a few more trivial changes for C++ compatibility
* command_graph.h: stop using "new" as a parameter name as that's a
reserved C++ keyword.
* module.h: avoid using C99 designated initializers since C++ doesn't
support them. This change hurts code readability quite considerably,
so we should try to find a better solution later.
* pw.h: remove unneeded empty structure to silence a C++ warning.