Octave: Use c++ 17

[jschueller]

see #616

[opoplawski]

This patch does not appear to be working for me in Fedora rawhide with octave 10.1.0. I still end up with -std=gnu++11. I that version logic really correct?

[jschueller]

you need #597 that removed the explicit c++11 standard,
then for fedora no need for #618 because default standard is already c++17 or higher with gcc 15

[jschueller]

@stevengj maybe we could release a 2.10.1 for the octave fixes, what do you think ?