`validation_flush_tests/getcoinscachesizestate` fails on RISCV-64 on master:
```
Running 394 test cases...
test/validation_flush_tests.cpp(99): error: in "validation_flush_tests/getcoinscachesizestate": check chainstate.GetCoinsCacheSizeState(tx_pool, MAX_COINS_CACHE_BYTES, 0) == CoinsCacheSizeState::OK has failed [1 != 0]

*** 1 failure is detected in the test module "Bitcoin Core Test Suite"
```
Haven't investigated why, yet. Apart from the architecture it could also be some dependency version causing the problem (this is a fedora rawhide install with very new versions of everything including gcc and boost).

Edit: see below, this is likely due to a newer `libstdc++`
{
    if (flags == 0) {
        return "";
    }
    std::string ret;
    std::map<std::string, unsigned int>::const_iterator it = mapFlagNames.begin();
    while (it != mapFlagNames.end()) {
        if (flags & it->second) {
            ret += it->first + ",";
        }
        it++;
    }
    return ret.substr(0, ret.size() - 1);
}
BOOST_FIXTURE_TEST_SUITE(transaction_tests, BasicTestingSetup)
BOOST_AUTO_TEST_CASE(tx_valid)