[llvm] [STLExtras] Introduce BinaryPredicateFunctor, [not_]equal_to (PR #175056)

[Jakub Kuderski via llvm-commits]

================
@@ -2157,6 +2157,30 @@ template <typename T> bool all_equal(std::initializer_list<T> Values) {
   return all_equal<std::initializer_list<T>>(std::move(Values));
 }
 
+template <typename ValT, typename RefT, typename BinaryPredicate>
+struct BinaryPredicateFunctor {
----------------
kuhar wrote:

The main difference is the quality of the implementation, IMO: `std::function` may heap allocate, while this is guaranteed not to. You can also make `PredT` be a template argument if you want to further restrict it for function pointers. 

https://github.com/llvm/llvm-project/pull/175056