[BOLT] Do not assign a LP to tail calls

Summary:
Do not assign a LP to tail calls. They are not calls in the
view of an unwinder, they are just regular branches. We were hitting an
assertion in BinaryFunction::removeConditionalTailCalls() complaining
about landing pads in a CTC, however it was in fact a
builtin_unreachable being conservatively treated as a CTC.

(cherry picked from FBD6564957)