Why does C++ program fail to compile on GCC and Clang?

Question

I thought this fine as it compiles on Visual Studio, but I found out when trying to compile on GCC and Clang that it might not be kosher:

#include <iostream>

#include <type_traits>

struct Bitfield
{

    template <typename first_arg_type, typename ... other_arg_types>
    static constexpr first_arg_type orTogether(first_arg_type firstArg, other_arg_types&& ... otherArgs)
    {
        if constexpr (std::is_enum_v<first_arg_type>)
        {
            using underlying_type = std::underlying_type_t<first_arg_type>;
            underlying_type result = static_cast<underlying_type>(firstArg);

            // Or with the rest
            ((result |= static_cast<underlying_type>(otherArgs)), ...);
            return static_cast<first_arg_type>(result);
        }
        else if constexpr (std::is_integral_v<first_arg_type>)
        {
            first_arg_type result = firstArg;

            // Or with the rest
            ((result |= otherArgs), ...);
            return result;
        }
        else {static_assert(false, "types must be either enum or integral");}
    }

};



int main()
{

}

The static_assert fires. The interesting thing is that it's not even instantiated. You can see on Godbolt that it compiles only on Visual Studio.