Thanks a lot Boud and Sven for the help and the how-to. Unfortunately,
the patch return me :
> deevad@deevad ~/koffice/koffice-build/krita/plugins/paintops/libbrush
> $ patch -p0 < ~/qtconcurrentmask.diff
> patching file kis_auto_brush.cpp
> Hunk #1 FAILED at 22.
> Hunk #2 FAILED at 34.
> Hunk #3 FAILED at 201.
> Hunk #4 FAILED at 254.
> 4 out of 4 hunks FAILED -- saving rejects to file kis_auto_brush.cpp.rej
> deevad@deevad ~/koffice/koffice-build/krita/plugins/paintops/libbrush $
But maybe this is too complicated for my user level to dive into , and I
prefer here to follow the advice of Sven ;