Seems neat, though I've not looked at mk/texinfo.mk closely.  Thanks
for the job!

One thing which comes to my mind hearing Texinfo is about the option
'--no-split' for makeinfo.  Nothing is documented about this, but I
believe there's a implicit consensus to use it where appropriate.  How
about adding MAKEINFO_ARGS and make it default to '--no-split'?

Regards,
Masao