ELF init_priority only orders constructors within a single module. All of
a shared object's initializers run before any of the executable's, so an
instrumented dependency .so emitting a zone from its static initializer
creates the main thread producer token against the zero-initialized
s_queue. The queue constructor then resets the producer list, orphaning
that producer: every zone emitted on the main thread from that point on
is enqueued into blocks no consumer ever iterates and silently lost,
while sampling (worker thread producer) keeps working.
Re-link such a producer right after the queue is constructed. In the
common case, where nothing was emitted during shared object init, this
merely constructs the main thread token eagerly.
