[tex-k] CTANGLE: support UTF-8

[Andreas Scherer]

Hi, Igor,

 > Modern compilers support UTF-8 identifiers.
Postponed until I upgrade to the next Kubuntu LTS:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67224

> new option +u
Although your patch works with plain 'ctangle.w', there's quite some 
work to do in order to integrate it smoothly in the CWEBbin/TL codebase.

I'll open an issue for 2022.

Thanks, Andreas