Error WebEngine include path when building QtCreator with cmake

I have 2 versions of Qt installed on my workstation : Qt 5.12.5 (installed from CentOS 8.2 repository) and Qt 5.15.1 (build and install from QT git repo).

I compile QtCreator with Qt 5.15.1.

To select the good version of QT, I export the variable Qt5_DIR before building:

export Qt5_DIR=/path/to/good_version_of_QT

When I build QtCreator, all include paths are good except include paths to QtWebEngineWidgets, QtWebEngineCore, QtWebChannel, QtPositioning

This causes an error when building help plugin.