Set parsing mode to C++14

Dear all,

I've read several times that KDevelop 5 had complete support for C++14,
which makes sense if using Clang, but I've never found how to set the
parser in C++14 mode. Every time I use a C++14 function of the standard
library it is not found (ex: std::begin, or std::make_unique), even though
it compiles just fine.

I'm using KDevelop 5.0.2 from the Arch repository and I have Clang 3.9.0.
I've tried generating the compile_commands.json file with CMake (the
CMakeLists.txt file contains set(CMAKE_CXX_STANDARD 14)) but it didn't help.

Thank you in advance!

Maverick