Clang reports 'file not found' on Windows [REG]

Re-installed creator 8.0,1 and renamed %APPDATA%\QtProject
Created a new QWidget project (with cmake) with wizard.
Moved #inclde <QApplication> above #include "qwidget".

Expected result:
A clean code that doesn't highlight errors if present.

Actual results:
It claims it cannot find QApplication.
(Example with an install 6.2.4 version - seems independent on Qt versions, though)

This problem came after an upgrade to 8.0.0 (but it was upgraded from a pretty old version - though I suspect it was using clang before, too).

I would like to have hand-test with clang and see what Qt executes, but it appears Qt doesn't write this anywhere.

With same version, I dont see this issue on Mac.