`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++`
#include <txmempool.h>
#include <validation.h>
#include <sync.h>
#include <test/util/setup_common.h>
#include <boost/test/unit_test.hpp>
BOOST_FIXTURE_TEST_SUITE(validation_flush_tests, BasicTestingSetup)
BOOST_AUTO_TEST_CASE(getcoinscachesizestate)
{
    BlockManager blockman{};
    CChainState chainstate{blockman};
    chainstate.InitCoinsDB( 1 << 10,  true,  false);
    WITH_LOCK(::cs_main, chainstate.InitCoinsCache());
    CTxMemPool tx_pool{};
    constexpr bool is_64_bit = sizeof(void*) == 8;