Problems building with not that old gcc versions since Boost 1.73

[reddwarf69]

Since 9379286, building

#include <boost/safe_numerics/safe_integer.hpp>
#include <fmt/format.h>
#include <fmt/ostream.h>

template<typename Stored,
         Stored Min,
         Stored Max,
         typename P,
         typename E>
struct fmt::formatter<
    boost::safe_numerics::safe_base<
        Stored, Min, Max, P, E
    >
> : fmt::ostream_formatter
{
};

void la()
{
    fmt::print("{}", boost::safe_numerics::safe<int>{ 4 });
}

with gcc 8.2-10.4 with -std=gnu++17 -Os -Wall fails. https://godbolt.org/z/Goc3er7vc

It's clearly a gcc bug, so it would be fair game to ignore it. But it affects Ubuntu 20.04.