When the built-in TBB is used is TBB_INCLUDE_DIRS is set to
To suppress warning the syntax
This leads the directory where the ROOT headers are to be marked as "system".
On MacOS, this means that the line
is added to the compilation line.
When clang generates dependency (at least with the flag we are using), it does *NOT* include any system header in the list produced by -MF.
In this case this means that NO ROOT headers is included in the .d files. Leading of course to corrupt builds as soon as any of the header that should have been listed is modied,
See for example