Similar issues have been reported for other project types. This one is specific to the Compilation Database Project Manager.

1. Enable the experimental Compilation Database Project Manager plugin
2. Create a minimal C++ project - I created a qmake-based one and I created it outside Qt Creator
3. Use e.g. compiledb or bear to create compile_commands.json under the project
4. Open the project through compile_commands.json in Qt Creator
5. Open the main C++ source

An infobar appears in the editor, saying:

Warning: The code model could not parse an included file, which might lead to incorrect code completion and highlighting, for example:
qglobal.h:1092:4: error: "You must build your code with position independent code if Qt was built with -reduce-relocations. " "Compile your code with -fPIC (-fPIE is not enough)."