qt.conf missing from Windows msvc2017 and 2017_64 variants, causing qmake to fail

Calling qmake from 5.13.0/msvc2017 under correct environment set up by "vcvarsall.bat x86" reports this error:

> qmake.exe -tp vc -r
Could not find qmake spec 'win32-msvc'.

This is because

> qmake.exe -query "QT_INSTALL_PREFIX"
c:/Users/qt/work/install

Which is caused by missing /bin/qt.conf with

[Paths]
Prefix = ..

But after adding the .conf, I get this:

> qmake.exe -tp vc -r
Error: Qt license file was not found!

I haven't found a solution for this problem, so Qt 5.13.0 is unusable on Windows.