I've been waiting with this anyway. Why? It works OK for Linux, etc. where reasonable version of Bison (3.0.4+) is easily available.
We use a lot of Bison features using all possible diagnostics it offers.

On Windows there's no way to even build Bison 3 for me, I spent time on that ;(
It's not maintained there.
So I'd freeze this patch until some solution is found. Cygwin as a dependency isn't a dream. For Kexi it would be bearable but well, we want KDb to be damn easily buildable for just Qt users...

RELATED:
After request from Christoph Feck I've added this:

"Make parser generation use custom target as before, so commands like 'make clean' won't modify the git files"

https://quickgit.kde.org/?p=kdb.git&a=commit&h=96cb7f99d7028aae8fa3226b0a2b3457a7cc8d82

Christoph's comment before that change:

(master) does no longer work since recent commits from Monday.

Compiling libkdb I get a failure about required bison 3.0.4 version
(installed is 2.7 as of openSUSE Leap 42.1).

Could you please check if it can still be made working with the old
bison version by committing all generated files?

Thanks,
Christoph Feck
KDE Quality Team

We will have to wait until Bison 3 is a mainstream.

It's potentially available on windows (not officially): https://github.com/lexxmark/winflexbison