As per title.
This one needs to come with a travis.yml upgrade.
Unless the plan is to ditch Travis and go with something else for CI.
I'll experiment a bit on that branch (https://github.com/ftrader-bitcoinabc/bitcoin-abc/commits/test_d294_require_cxx_14). So far, looks like we might need Travis support to even get it working despite their published instructions.
C++14 is already several years old.
CI on each patch is not important enough for it to be worth it. Many projects do not run CI on each patch and are doing just fine (LLVM being one of them). If a contributor keeps submitting patches that breaks the build, the right solution is to fire that contributor. Someone not testing his own patch is problem that CI on each patch can only hide, not fix.
First and foremost, we need CI on master.
Ubuntu Yakkety (16.10) and Debian 9 come with g++ versions that are able to build with this C++14 requirement.
To properly support C++14, we need to upgrade the gitian build which currently uses Ubuntu 16.04 (Trusty).