Opening an issue after some recent IRC discussion about moving to requiring C++14.

GCC:

C++14 is available from GCC 5, and is the default mode in GCC 6.1.
"The default mode for C++ is now -std=gnu++14 instead of -std=gnu++98.".
We currently require GCC 4.8+.

Clang:

C++14 is available from Clang 3.4+.
We currently require Clang 3.3+.

Usage:

We currently already use shared mutex.