Log Message:
cmake: specifically test for some C++17 features.

In case the compiler used advertises C++17 but uses a C++ library that
lacks some features, we'll need specific testing.

Unbreaks the build for: libstdc++ from 5.4 and clang 7.0
Submitted upstream: https://gitlab.kitware.com/cmake/cmake/merge_requests/3030/diffs
(No response yet)

From wizermil.