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"
```
{
    constexpr uint64_t min_disk_space = 52428800; 
    uint64_t free_bytes_available = fs::space(dir).available;
    return free_bytes_available >= min_disk_space + additional_bytes;
}
/**
 * Interpret a string argument as a boolean.
 *
 * The definition of atoi() requires that non-numeric string values like "foo",
 * return 0. This means that if a user unintentionally supplies a non-integer
 * argument here, the return value is always false. This means that -foo=false
 * does what the user probably expects, but -foo=true is well defined but does
 * not do what they probably expected.
 *
 * The return value of atoi() is undefined when given input not representable as
 * an int. On most systems this means string value between "-2147483648" and
 * "2147483647" are well defined (this method will return true). Setting
 * -txindex=2147483648 on most systems, however, is probably undefined.
 *
 * For a more extensive discussion of this topic (and a wide range of opinions
 * on the Right Way to change this code), see PR12713.
 */
static bool InterpretBool(const std::string& strValue)
{
    if (strValue.empty())
        return true;
    return (atoi(strValue) != 0);
}
class ArgsManagerHelper {