Fails to build with protobuf 3.6.0 due to c++11 requirement

[eli-schwartz]

While rebuilding mumble with the new protobuf version for Arch Linux, I discovered it would not build due to protocolbuffers/protobuf#2780

The fix is to add CONFIG+=' c++11 ', but it would probably make sense to set this automatically rather than force users to figure out the need for this themselves after it errors the first time.

[radioactiveman]

This should already be fixed with #2630. The AUR package mumble-git also does not require the mentioned workaround.

[eli-schwartz]

But that's not true, since the PR you reference in fact sets a default of c++98 and not c++11. With current protobuf this simply does not work at all.

As for why it did not detect support automatically and raise the bar to c++11, I guess that's because it is checking QT_CONFIG which for qt5 includes c++11 c++14 c++1z but for qt4 includes none of that. Now which one is being used for the two-year-old stable release?

[Krzmbrzl]

Is this still relevant? I thought that Mumble now switched to cpp11. Not sure though.

@davidebeatrici or @Kissaki do you have a better overview on this?

[davidebeatrici]

I confirm that we switched to C++11, thank you for bringing this up.