I don’t think that this is caused by the GCC6 update.  The error is

error: no matching function for call to 'KConfigGroup::deleteEntry(const char [21], bool)' configgroup.deleteEntry("First use of Kwallet", false);

And this seems more the result of latest kdelibs changes. My guess would be that finally kvpnc got rebuild after quite a long time and now we suddenly have the failure. 

As that kvpnc is also dead upstream, I would suggest to remove it from Tumbleweed.

(In reply to Raymond Wooninck from comment #1)
> I don’t think that this is caused by the GCC6 update.  The error is
> 
> error: no matching function for call to 'KConfigGroup::deleteEntry(const
> char [21], bool)' configgroup.deleteEntry("First use of Kwallet", false);
> 
> And this seems more the result of latest kdelibs changes. My guess would be
> that finally kvpnc got rebuild after quite a long time and now we suddenly
> have the failure. 

No, that's not caused by a recent change in kdelibs.

KConfigGroup::deleteEntry expects as second parameter enum KConfigBase::WriteConfigFlag in kdelibs4, not bool like in kdelibs3.
That's a KDE3->KDE4 porting bug it seems.

I suppose earlier GCC versions just didn't complain about that.

> As that kvpnc is also dead upstream, I would suggest to remove it from
> Tumbleweed.

Well, it's not completely dead apparently.
There have been changes in upstream SVN a few months ago, including fixes for GCC6.
This particular issue has been fixed as well:
https://websvn.kde.org/trunk/playground/network/kvpnc/src/kvpncconfig.cpp?r1=1449161&r2=1452683

I will have a look at this over the weekend...

(In reply to Wolfgang Bauer from comment #2)
> I will have a look at this over the weekend...
Thanks, Raymond, for beating me on that one. ;-)

https://build.opensuse.org/request/show/403028

I suppose we can close this bug report then as well...