iwyu: fatal error: ‘stddef.h’ file not found

Written by  on September 8, 2021

Include-what-you-use and Qt are not friends. iwyu-support in QtCreator is requested for a while, nobody cares.
So I installed it via apt; set an override to make and reran the build-process on a cleaned project:

Result: more than fifty errors like “fatal error: ‘stddef.h’ file not found”.
Some said that clang is missing (because that header is part of the installed package, my clang was 12 – iwyu was built against 11).
So the solution is: