broadcom/compiler: disallow tsy barrier in thrsw delay slots

A TSY barrier becomes effective at the point of the next thread switch, so if we have one coming after a previous thread switch we need to be careful not to emit it in its delay slots, or we would be effectively moving the barrier earlier than intended.

Fixes simulator assert crash in: dEQP-VK.graphicsfuzz.two-for-loops-with-barrier-function