References to symbols in dylibs work very similarly regardless of
whether the symbol is a TLV. The main difference is that we have a
separate __thread_ptrs section that acts as the GOT for these
We can identify thread-locals in dylibs by a flag in their export trie
entries, and we cross-check it with the relocations that refer to them
to ensure that we are not using a GOT relocation to reference a
thread-local (or vice versa).