This is being emitted with [GCC 10.2.1](https://packages.debian.org/bullseye/g++-arm-linux-gnueabihf), in some CI jobs: i.e https://github.com/bitcoin/bitcoin/pull/25972/checks?check_run_id=12423693655, or https://github.com/bitcoin/bitcoin/pull/25972/checks?check_run_id=12423693651 (where we actually turn on all our warning flags with depends builds).
```bash
In file included from test/miniscript_tests.cpp:19:
./script/miniscript.h:1197:71: error: comparison of integers of different signs: 'typename iterator_traits<int *>::difference_type' (aka 'int') and 'const uint32_t' (aka 'const unsigned int') [-Werror,-Wsign-compare]
                    return std::count(subs.begin(), subs.end(), true) >= node.k;
                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~
test/miniscript_tests.cpp:346:34: note: in instantiation of function template specialization 'miniscript::Node<CPubKey>::IsSatisfiable<(lambda at test/miniscript_tests.cpp:346:48)>' requested here
        bool satisfiable = node->IsSatisfiable([](const Node&) { return true; });
                                 ^
1 error generated.
```

cc @darosior 
Availability avail = ctx.Sign(node.keys[i], sig);
                        
                        auto sat = InputStack(std::move(sig)).SetWithSig().SetAvailable(avail);
                        
                        
                        
                        std::vector<InputStack> next_sats;
                        next_sats.push_back(sats[0]);
                        for (size_t j = 1; j < sats.size(); ++j) next_sats.push_back(sats[j] | (std::move(sats[j - 1]) + sat));
                        next_sats.push_back(std::move(sats[sats.size() - 1]) + std::move(sat));
                        
                        sats = std::move(next_sats);
                    }
                    
                    InputStack nsat = ZERO;
                    for (size_t i = 0; i < node.k; ++i) nsat = std::move(nsat) + ZERO;
                    assert(node.k <= sats.size());
                    return {std::move(nsat), std::move(sats[node.k])};
                }
                case Fragment::THRESH: {
                    
                    
                    
                    std::vector<InputStack> sats = Vector(EMPTY);
                    for (size_t i = 0; i < subres.size(); ++i) {
                        
                        auto& res = subres[subres.size() - i - 1];