The '__' prefix should only be used for the parts of the ORC runtime that
implement compiler / loader runtime details (e.g. ORC-RT's __tlv_get_addr
implementations).
This patch only fixes the public API. Future changes will fix internal names.
The ORC runtime isn't used by clang -- the prefix was just cargo-culted with
the rest of the XRay config when the ORC runtime was introduced. We now want to
make parts of it available for clients to link directly, so this seems like a
good time to fix the name.
