Since std::forward is nothing more than a cast, part of STL and not the
language itself, it's easy to provide a custom implementation if one
wishes not to include the entirety of <utility>.
Added flag (ForwardFunction) provides a way to continue using this
essential check even with the custom implementation of forwarding.
---------
Co-authored-by: EugeneZelenko <eugene.zelenko@gmail.com>
Warns when a function accepting a forwarding reference does anything besides
forwarding (with std::forward) the parameter in the body of the function.
Reviewed By: PiotrZSL
Differential Revision: https://reviews.llvm.org/D146921
