`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++`
{
    
    unsigned char ch[] = {0x01, 0x00, 0x00, 0x00, 0x01, 0x6b, 0xff, 0x7f, 0xcd, 0x4f, 0x85, 0x65, 0xef, 0x40, 0x6d, 0xd5, 0xd6, 0x3d, 0x4f, 0xf9, 0x4f, 0x31, 0x8f, 0xe8, 0x20, 0x27, 0xfd, 0x4d, 0xc4, 0x51, 0xb0, 0x44, 0x74, 0x01, 0x9f, 0x74, 0xb4, 0x00, 0x00, 0x00, 0x00, 0x8c, 0x49, 0x30, 0x46, 0x02, 0x21, 0x00, 0xda, 0x0d, 0xc6, 0xae, 0xce, 0xfe, 0x1e, 0x06, 0xef, 0xdf, 0x05, 0x77, 0x37, 0x57, 0xde, 0xb1, 0x68, 0x82, 0x09, 0x30, 0xe3, 0xb0, 0xd0, 0x3f, 0x46, 0xf5, 0xfc, 0xf1, 0x50, 0xbf, 0x99, 0x0c, 0x02, 0x21, 0x00, 0xd2, 0x5b, 0x5c, 0x87, 0x04, 0x00, 0x76, 0xe4, 0xf2, 0x53, 0xf8, 0x26, 0x2e, 0x76, 0x3e, 0x2d, 0xd5, 0x1e, 0x7f, 0xf0, 0xbe, 0x15, 0x77, 0x27, 0xc4, 0xbc, 0x42, 0x80, 0x7f, 0x17, 0xbd, 0x39, 0x01, 0x41, 0x04, 0xe6, 0xc2, 0x6e, 0xf6, 0x7d, 0xc6, 0x10, 0xd2, 0xcd, 0x19, 0x24, 0x84, 0x78, 0x9a, 0x6c, 0xf9, 0xae, 0xa9, 0x93, 0x0b, 0x94, 0x4b, 0x7e, 0x2d, 0xb5, 0x34, 0x2b, 0x9d, 0x9e, 0x5b, 0x9f, 0xf7, 0x9a, 0xff, 0x9a, 0x2e, 0xe1, 0x97, 0x8d, 0xd7, 0xfd, 0x01, 0xdf, 0xc5, 0x22, 0xee, 0x02, 0x28, 0x3d, 0x3b, 0x06, 0xa9, 0xd0, 0x3a, 0xcf, 0x80, 0x96, 0x96, 0x8d, 0x7d, 0xbb, 0x0f, 0x91, 0x78, 0xff, 0xff, 0xff, 0xff, 0x02, 0x8b, 0xa7, 0x94, 0x0e, 0x00, 0x00, 0x00, 0x00, 0x19, 0x76, 0xa9, 0x14, 0xba, 0xde, 0xec, 0xfd, 0xef, 0x05, 0x07, 0x24, 0x7f, 0xc8, 0xf7, 0x42, 0x41, 0xd7, 0x3b, 0xc0, 0x39, 0x97, 0x2d, 0x7b, 0x88, 0xac, 0x40, 0x94, 0xa8, 0x02, 0x00, 0x00, 0x00, 0x00, 0x19, 0x76, 0xa9, 0x14, 0xc1, 0x09, 0x32, 0x48, 0x3f, 0xec, 0x93, 0xed, 0x51, 0xf5, 0xfe, 0x95, 0xe7, 0x25, 0x59, 0xf2, 0xcc, 0x70, 0x43, 0xf9, 0x88, 0xac, 0x00, 0x00, 0x00, 0x00, 0x00};
    std::vector<unsigned char> vch(ch, ch + sizeof(ch) -1);
    CDataStream stream(vch, SER_DISK, CLIENT_VERSION);
    CMutableTransaction tx;
    stream >> tx;
    TxValidationState state;
    BOOST_CHECK_MESSAGE(CheckTransaction(CTransaction(tx), state) && state.IsValid(), "Simple deserialized transaction should be valid.");
    
    tx.vin.push_back(tx.vin[0]);
    BOOST_CHECK_MESSAGE(!CheckTransaction(CTransaction(tx), state) || !state.IsValid(), "Transaction with duplicate txins should be invalid.");
}
static std::vector<CMutableTransaction>