Detect C++17 [[attribute]] compile feature
It will be useful to be able to detect such attributes as [[discard]] or [[maybe_unused]]. For example Visual Studio supports it only form version 15.3.
If it will be approved, I could implement it.
They were defined in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0068r0.pdf
Edited by Denys Senkin