KOS_OP_POP_WIND
Style: NOARG.
Stack: Pops TOS (the body result) into the wind node, pops wind from the dynamic chain, and runs the after thunk (if entered and non-null) via kos_dyn_wind_unwind; the body result is delivered to the revealed segment when the thunk completes (or immediately when there is none). May return KOS_DYN_UNWIND_ASYNC_STARTED when the thunk pushes a frame.
Invariants: Dyn top must be KOS_DYN_WIND; otherwise RuntimeError.