[C++] cxx_status and support in Clang

Here is the list of current C++ implementation status and support in Clang as per Aug 2017.
You can find the complete list of features and minimum Clang version with support on the source page: https://clang.llvm.org/cxx_status.html

C++11 implementation status
Clang 3.3 and later implement all of the ISO C++ 2011 standard. By default, Clang builds C++ code according to the C++98 standard, with many C++11 features accepted as extensions. You can use Clang in C++11 mode with the -std=c++11 option. Clang’s C++11 mode can be used with libc++ or with gcc’s libstdc++.

C++14 implementation status
Clang 3.4 and later implement all of the ISO C++ 2014 standard.

You can use Clang in C++14 mode with the -std=c++14 option (use -std=c++1y in Clang 3.4 and earlier).

C++17 implementation status
Clang 5 and later implement all the features of the C++ 2017 Draft International Standard.
You can use Clang in C++17 mode with the -std=c++17 option (use -std=c++1z in Clang 4 and earlier).

C++2a implementation status
Clang has experimental support for some proposed features of the C++ standard following C++17, provisionally named C++2a. Note that support for these features may change or be removed without notice, as the draft C++2a standard evolves.
You can use Clang in C++2a mode with the -std=c++2a option.

More technical specifications and standing documents on the source page: https://clang.llvm.org/cxx_status.html