Apply pull request grisumbras#32 to fix MSVC 2022 compilation error

Author: Tim Crews

include/flags/flags.hpp

@@ -83,7 +83,13 @@ template <class E> class flags {
   template <class ... Args>
   flags(enum_type e, Args ... args) noexcept : flags{e, args...} {}
 
-
+  template <class FwIter>
+  flags(FwIter b, FwIter e,
+        typename convertible<decltype(*std::declval<FwIter>())>::type = nullptr)
+  noexcept(noexcept(std::declval<flags>().insert(std::declval<FwIter>(),
+                                                 std::declval<FwIter>())))
+  : val_(0)
+  { insert(b, e); }
 
   constexpr explicit operator bool() const noexcept { return val_ != 0; }