std::invoke_result is missing in libc++?

Hi,

Trying to build my code in C++17 mode with clang fails with missing
std::invoke_result_t in libc++.
See http://en.cppreference.com/w/cpp/types/result_of

Grepping master branch does not give any matches.
Am I missing something or there's no invoke_result implementation?

The C++17 support in libc++ is a work-in-progress. The current status is described here: http://libcxx.llvm.org/cxx1z_status.html