Add option to use OneTBB for multithreading

[jdumas]

It'd be great to be able to use OneTBB as the multithreading backend. Using the same scheduler in a larger app really helps avoiding oversubscription in general. When I was at nTopology I did some work in this direction in our geogram fork at the time (using an older TBB version). Maybe this can provide some inspiration. One important change is that TBB's spinlock cannot be initialized with an assignment constructor (foo = x syntax), so this requires a few extra changes in the rest of Geogram.