configure: Use c++17

This is needed to start using c++17 libraries and the code should
already be trivially compatible. We can't move away from
std::experimental::filesystem yet as that requires gcc8+.

Tested:
    Project still builds in the unit test environment although no tests
    are actually run.

Change-Id: I4db0bfe3d42be58d5296eddf5dea5383b7847374
Signed-off-by: William A. Kennington III <wak@google.com>
1 file changed