restoring macOS compatibility

The code can be compiled with clang on macOS. TABs in FindTBB.cmake have been cleaned.

Some tests of mirrors generate segfaults (on macOS).

44/67 Test #47: mirrors/tests/mparams/loop6.py ............***Exception: SegFault109.68 sec 56/67 Test #53: mirrors/tests/mparams/mparams.py ..........***Exception: SegFault 22.62 sec 65/67 Test #43: mirrors/tests/mparams/loop2.py ............***Exception: SegFault308.35 sec

Other failures should be investigated further:

12/67 Test #12: flow/tests/channel.py .....................***Failed 1.75 sec (problem with my installation of MUMPS on my mac? - works well on Ubuntu) 33/67 Test #27: heat/tests/fe2/heat_mpi.py ................***Failed 9.75 sec