There is build problem on mac11 nodes:

FAILED: core/thread/G__Thread.cxx lib/Thread.pcm 
/Users/sftnight/build/workspace/root-pullrequests-build/build/include/ROOT/TReentrantRWLock.hxx:26:10: fatal error: 'tbb/enumerable_thread_specific.h' file not found

https://lcgapp-services.cern.ch/root-jenkins/job/root-pullrequests-build/115867/console

It is because of that PR: #7260

It exposes TBB to public includes - via ROOT/TReentrantRWLock.hxx file.

First of all one should specify that Thread library depend on TBB builtins - thats easy.

But also one should export TBB_INCLUDE_DIRS and TBB_CXXFLAGS as INTERFACE (not PRIVATE) properties of Thread library. Do we want this?