Now that templates instantiations are no longer emitted for all modules that even blink at them they seem to break due to being linkonce (if compiled with any optimization level > 0), so let's give them weak linkage instead. The difference is that unreferenced linkonce symbols can be deleted, while weak symbols need to be preserved.

module tangotests.sync2;

class Lock
{
}

const Lock lock;

static this()
{
    lock = new Lock;
}

void main()
{
    size_t id;
    synchronized(lock) id = 2;
}