We're using a lot of space on the free lists. Each vector is three words, and we have two of them. Switch to a single linked list. We only need one list, as both kinds of pointers just get free()'d. A linked list optimizes for the common case where the list is empty. This takes us from six words to one.
Also make ReaderCount, ElementCount, and ElementCapacity uint32_ts. The size_ts were unnecessarily large and this saves some space on 64-bit systems.
While we're in there, add 0/NULL initialization to all elements. The current use in the runtime is unaffected (it's statically allocated) but the local variables used in the test were tripping over this.
One of our Ubuntu 16.04 CI machines is seeing different variations
of the std::__once_call_impl<>() constructor than the ones we're already filtering out.
Resolves rdar://64267618
The Swift standard library should not export weak symbols. Ensure that
no public weak symbols are defined in the standard library by adding a
test case. This would have identified the issue introduced by the
recent changes for the runtime.
