File size checks fails and I haven't figured out why, but next I'd look into how `posix_fallocate` works on alpine linux.

Log:

```
$ cat /etc/alpine-release 
3.9.2

$ git log --oneline -1
e45b7f20e Merge #15618: refactor: Remove unused function

$ ./src/test/test_bitcoin -t flatfile_tests
Running 4 test cases...
Version using posix_fallocate
test/flatfile_tests.cpp(94): error: in "flatfile_tests/flatfile_allocate": check fs::file_size(seq.FileName(FlatFilePos(0, 0))) == 100 has failed [0 != 100]
test/flatfile_tests.cpp(98): error: in "flatfile_tests/flatfile_allocate": check fs::file_size(seq.FileName(FlatFilePos(0, 99))) == 100 has failed [0 != 100]
Version using posix_fallocate
test/flatfile_tests.cpp(102): error: in "flatfile_tests/flatfile_allocate": check fs::file_size(seq.FileName(FlatFilePos(0, 99))) == 200 has failed [0 != 200]
Version using posix_fallocate
test/flatfile_tests.cpp(116): error: in "flatfile_tests/flatfile_flush": check fs::file_size(seq.FileName(FlatFilePos(0, 1))) == 100 has failed [0 != 100]

*** 4 failures are detected in the test module "Bitcoin Core Test Suite"
```
* false.
 *
 * Where an option was negated can be later checked using the
 * IsArgNegated() method. One use case for this is to have a way to disable
 * options that are not normally boolean (e.g. using -nodebuglogfile to request
 * that debug log output is not sent to any file at all).
 */
static bool InterpretNegatedOption(std::string& key, std::string& val)
{
    assert(key[0] == '-');
    size_t option_index = key.find('.');
    if (option_index == std::string::npos) {
        option_index = 1;
    } else {
        ++option_index;
    }
    if (key.substr(option_index, 2) == "no") {
        bool bool_val = InterpretBool(val);
        key.erase(option_index, 2);
        if (!bool_val ) {
            
            LogPrintf("Warning: parsed potentially confusing double-negative %s=%s\n", key, val);
            val = "1";
        } else {
            return true;
        }
    }
    return false;
}
ArgsManager::ArgsManager() :