While testing 17270 I noticed that master (bdda137878904e9401a84e308ac74c93c2ef87c1) does not run on NetBSD. I assume this started after #17085 changed the fallback locale from `C` to `C.UTF-8`. There doesn't seem to be a `C.UTF-8` locale on NetBSD.

```bash
src/bitcoind
terminate called after throwing an instance of 'std::runtime_error'
  what():  locale::facet::_S_create_c_locale name not valid
Abort trap (core dumped)
```

`LC_ALL=C src/bitcoind` works, `LC_ALL=en_US.UTF-8 src/bitcoind` does not.

```bash
locale
LANG=""
LC_CTYPE="en_US.UTF-8"
LC_COLLATE="C"
LC_TIME="C"
LC_NUMERIC="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_ALL=""
```
{
    if (IsArgNegated("-settings")) {
        return false;
    }
    if (filepath) {
        std::string settings = GetArg("-settings", BITCOIN_SETTINGS_FILENAME);
        *filepath = fsbridge::AbsPathJoin(GetDataDirNet(), temp ? settings + ".tmp" : settings);
    }
    return true;
}
static void SaveErrors(const std::vector<std::string> errors, std::vector<std::string>* error_out)
{
    for (const auto& error : errors) {
        if (error_out) {
            error_out->emplace_back(error);
        } else {
            LogPrintf("%s\n", error);
        }
    }
}
bool ArgsManager::ReadSettingsFile(std::vector<std::string>* errors)