[Bug libstdc++/78991] std::sort and std::unique can not use std::function with clang++ -std=c++14

[daiw at gmx dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78991

--- Comment #2 from Tobias <daiw at gmx dot net> ---
Thanks. The evidence you collected shows quite clear, that it probably is a
problem with clang.
So I now posted it here: https://llvm.org/bugs/show_bug.cgi?id=31537