Fix potential memory leak when a thread is disabled.
Fix potential memory leak when a thread is disabled.

A disable statement can terminate a thread whilst it still has
local variables on the stack (e.g. the loop counter for a repeat
statement). We need to clear the thread stacks when this happens.

CastMi/iverilog,CastMi/iverilog,themperek/iverilog,CastMi/iverilog,themperek/iverilog,themperek/iverilog