[Bug libstdc++/65942] [5/6 Regression] [C++14] cannot use std::function as comparator in algorithms

[harald at gigawatt dot nl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65942

--- Comment #12 from Harald van Dijk <harald at gigawatt dot nl> ---
(In reply to Harald van Dijk from comment #11)
> The programs in my comment here are accepted by G++ 4.5.4 (with -std=c++0x),
> and rejected by 4.6.4 and later.

But as G++ 4.5 recognises but simply ignores the constexpr keyword, it's not
really a regression. 4.6 is the first that actually implements constexpr
functions, and it was broken in that version already.