RFR: Enable TLHS by default (again)

[Aleksey Shipilev]

On 11/14/2018 04:56 PM, Roman Kennke wrote:
> Do we want to finally enable TLHS for good? Or do we considere too risky
> compared to (almost zero immediate) usefulness? It'd allow some more
> concurrent processing going forward.

I think it is too risky without apparent benefit, at this point. Adding the simple regression test
with TLHS specifically enabled would be nice, though.

-Aleksey