QSettings sync fails on Android 7 and 8

We encountered a bug on Android 7 and 8 when using QSettings/QTemporaryFile. The QSettings cannot be written. When calling sync the settings file cannot be created.

Steps to reproduce:

1. Create QSettings object
2. Set value
3. Call sync

Our current understanding of the problem:

In this commit https://github.com/qt/qtbase/commit/189e9c93d7ed42202ad51507c8944d64e9a7888d the function createUnnamedFile was introduced to QTemporaryFile. It uses a Linux feature to create a temporary file without a filepath. QSettings seems to use QTemporaryFile. When calling sync the call to the libc function "linkat" fails. We could temporarily fix the problem by returning "CreateUnnamedFileStatus::NotSupported" in src/corelib/io/qtemporaryfile.cpp::createUnnamedFile() .