Build Qt Creator 3.6 on newer distros

umod.47

Hello.
I'm having a long problem with Qt Creator 4+, that fails to autocomplete properly.
https://forum.qt.io/topic/90166/qt-creator-autocomplete-fails-to-work-with-ui/7
TL;DR:

With CLang code model enabled, Qt additions, like SIGNAL() and SLOT() macro don't work, as well as some other things like redefining function from parent class in child class.
With CLang code model disabled, all Qt additions work as required, but autocompletion fails to work with ui classes (something like ui->pushButton fails to autocomplete further).

I'm using Arch Linux, so older version of Qt Creator is not available to me, I have to build it from the source.
I was able to find Qt Creator source and build it on my system:

$ uname -a
Linux Terraniux 4.20.12-arch1-1-ARCH #1 SMP PREEMPT Sat Feb 23 15:11:34 UTC 2019 x86_64 GNU/Linux
$ qmake --version
QMake version 3.1
Using Qt version 5.12.1 in /usr/lib

... usind guide from this link:
https://wiki.qt.io/Building_Qt_Creator_from_Git

I've also deleted all configuration files from newer version of Qt Creator, using this guide:
https://doc.qt.io/qtcreator/creator-quick-tour.html#location-of-settings-files

Still, Qt Creator 3.6 is able to start without installation, but if I try to open settings or a project, everything crashes. This is what I see in the console output:

$ ./bin/qtcreator
MimeDatabase: Error loading :/qt-project.org/qmime/freedesktop.org.xml
Cannot open :/qt-project.org/qmime/freedesktop.org.xml: No such file or directory
Ошибка сегментирования (стек памяти сброшен на диск)

The first 2 messages appear at the start of the application.
What should I do to run Qt Creator 3.6 on newer systems?
How to find what this segmentation fault is caused by?