[rttr] rttr provided with vcpkg cannot be build with C++20

[pozemka]

Is your feature request related to a problem? Please describe.
When I create basic HelloWorld with rttr it doesn't build if I choose C++ 20 in my Cmake file (set(CMAKE_CXX_STANDARD 20)).
It does build if I use C++17.
If I download RTTR directly from RTTR Github and apply simple patch I can compile helloworld.

Proposed solution
My proposal is to upadte RTTR in vcpkg to the latest commit and make necessary changes so programs that using rttr and C++20 could be build.

Describe alternatives you've considered
Fine alternative is to add rtti to sourcetree of my project and use local version instead of provided by vcpkg.
I also managed to change rttr's portfile.cmake and related patches to do what I want but it should be carefully maintained every time I update vckg subrepo.

Additional context
It seems that RTTI is abandoned by it's creator. Lots of unmerged PRs and unanswered tickets 😥

Mentioned helloworld and patch to rttr
Helloworld from here

#include <rttr/registration>
static void f() { std::cout << "Hello World" << std::endl; }
using namespace [rttr](https://www.rttr.org/doc/master/namespacerttr.html);
[RTTR_REGISTRATION](https://www.rttr.org/doc/master/registration_8h.html#ac6326400f16225ee15b52eabcaae8130)
{
    using namespace [rttr](https://www.rttr.org/doc/master/namespacerttr.html);
    [registration::method](https://www.rttr.org/doc/master/classrttr_1_1registration.html#ae37c7b97c7b6cc20d88d34d8aa26e12b)("f", &f);
}
int main()
{
    [type::invoke](https://www.rttr.org/doc/master/classrttr_1_1type.html#aa9d399ace70b2799d7bb6dab147e09a7)("f", {});
}
// outputs: "Hello World"

Patch is:

diff --git a/src/rttr/detail/misc/flat_map.h b/src/rttr/detail/misc/flat_map.h
index 767c97b..a3250a4 100644
--- a/src/rttr/detail/misc/flat_map.h
+++ b/src/rttr/detail/misc/flat_map.h
@@ -36,7 +36,7 @@
 #include <utility>
 #include <functional>
 #include <algorithm>
-#include <ciso646> // _LIBCPP_VERSION
+// #include <ciso646> // _LIBCPP_VERSION //warning C4996: '_Header_ciso646': warning STL4036: <ciso646> is removed in C++20.
 
 namespace rttr
 {

Just in case error message when building with C++20:

rtti1\out\build\x64-Debug\vcpkg_installed\x64-windows\include\rttr\detail\registration\bind_impl.h(358): error C2760: syntax error: ')' was unexpected here; expected 'expression'
rtti1\out\build\x64-Debug\vcpkg_installed\x64-windows\include\rttr/detail/registration/bind_impl.h(349): note: This diagnostic occurred in the compiler generated function 'std::unique_ptr<rttr::detail::property_wrapper_base,std::default_deleterttr::detail::property_wrapper_base> rttr::registration::bindrttr::detail::prop,Class_Type,A,acc_level::create_default_property(rttr::string_view,Acc)'
rtti1\out\build\x64-Debug\vcpkg_installed\x64-windows\include\rttr/detail/registration/bind_impl.h(428): note: see reference to class template instantiation 'rttr::registration::bindrttr::detail::prop,Class_Type,A,acc_level' being compiled