it seems that the clangd code model does not work with unity builds anymore

Steps to reproduce:

• configure qt with unity builds (QT_UNITY_BUILD=ON)

observations:

• opening any cpp files, e.g. qcoreevent.cpp, there is a warning headline: "This file is not part of any project"
• code navigation is incomplete: "find references to symbol under cursor" on `QCoreApplication::aboutToQuit` does not find the instance in `QCoreApplication::exit`

when reconfiguring the project without unity builds (e.g. QT_UNITY_BUILD=OFF for qt), it works as intended.

it used to be a problem before, but was fixed last year (QTCREATORBUG-26822). seems to be a recent regression