6bb075a53f
It's now available and allows us to have a better default environment, with GCC 7.4.0 and Clang 7. We now need GCC 7+ for C++17 support so it's more efficient to upgrade the image than to install it on Ubuntu 16.04 (xenial). Also fixes a couple -Wdeprecated-declarations warnings on macOS now that we build against macOS 10.12.