spsc-queue: don't statically construct the queue

spsc-queue: don't statically construct the queue

Our model-checker doesn't support constructors which perform
model-checking actions (e.g, atomic initialization) at load time (e.g.,
in a static execution of the constructor), since this happens before the
model-check object is created. Maybe we'll fix that in the future, but
for now, don't construct the queue at load time.