Previously, they were only created when we had any TLS segment.
This meant that while the symbol existed, the global itself wouldn't.
The result of this was a crash during symbol names writing as it
would attempt to write the symbol name of a global that didn't exist.
Now we always create them, and instead update its `init` value during
`setupMemory`.
In the future, the entire symbol (and global) will be removed by
the garbage collector.
