C++ 17 fixes and deprecations

[John Ralls]

C++ 17 is almost done and many of the changes are already in the latest versions of gcc and clang. This blog post:
http://www.bfilipek.com/2017/05/cpp17-details-fixes-deprecation.html <http://www.bfilipek.com/2017/05/cpp17-details-fixes-deprecation.html>

Details some significant behavior changes that we'll need to be careful about when using those new versions so that we don't accidentally break the build with older compilers.

Regards,
John Ralls