When compiling without external signer support, the resulted `bench_bitcoin.exe` fails on Windows:
```
>.\bench_bitcoin.exe -filter=AddrManSelectByNetwork
Error: bad optional access
```

Steps to reproduce the failure:
- cross compiling on Ubuntu 22.04:
```
$ make -j $(nproc) -C depends HOST=x86_64-w64-mingw32 NO_QT=1
$ ./autogen.sh
$ ./configure CONFIG_SITE=$PWD/depends/x86_64-w64-mingw32/share/config.site --disable-external-signer
$ make -j $(nproc)
```
- compiling natively on Windows:

Apply the diff as follows:
```diff
--- a/build_msvc/bitcoin_config.h.in
+++ b/build_msvc/bitcoin_config.h.in
@@ -41,9 +41,6 @@
 /* Define this symbol to enable ZMQ functions */
 #define ENABLE_ZMQ 1
 
-/* define if external signer support is enabled (requires Boost::Process) */
-#define ENABLE_EXTERNAL_SIGNER /**/
-
 /* Define to 1 if you have the declaration of `be16toh', and to 0 if you
    don't. */
 #define HAVE_DECL_BE16TOH 0
```
Then
```
>py -3 build_msvc\msvc-autogen.py
>msbuild build_msvc\bitcoin.sln -property:Configuration=Release -verbosity:minimal
>src\bench_bitcoin.exe -filter=AddrManSelectByNetwork
Error: bad optional access
```

---

The failure does not manifest itself when running `bench_bitcoin.exe` using Wine on Linux.
}
    
    CCoinsView coins_view;
    CCoinsViewCache coins_cache(&coins_view);
    for (const auto& input_transaction : input_transactions) {
        AddCoins(coins_cache, *input_transaction.get(), input_height);
    }
    
    std::map<COutPoint, Coin> input_coins;
    CAmount inputs_amount{0};
    for (const auto& outpoint_to_spend : inputs) {
        
        Coin utxo_to_spend;
        assert(coins_cache.GetCoin(outpoint_to_spend, utxo_to_spend));
        input_coins.insert({outpoint_to_spend, utxo_to_spend});
        inputs_amount += utxo_to_spend.out.nValue;
    }
    
    int nHashType = SIGHASH_ALL;
    std::map<int, bilingual_str> input_errors;
    assert(SignTransaction(mempool_txn, &keystore, input_coins, nHashType, input_errors));
    CAmount current_fee = inputs_amount - std::accumulate(outputs.begin(), outputs.end(), CAmount(0),
        [](const CAmount& acc, const CTxOut& out) {
        return acc + out.nValue;
    });
    
    if (feerate.has_value()) {
        assert(fee_output.has_value());
        assert(fee_output.value() < mempool_txn.vout.size());
        CAmount target_fee = feerate.value().GetFee(GetVirtualTransactionSize(CTransaction{mempool_txn}));