PR19553: Memory leak in RuntimeDyldELF::createObjectImageFromFile

This starts in MCJIT::getSymbolAddress where the
unique_ptr<object::Binary> is release()d and (after a cast) passed to a
single caller, MCJIT::addObjectFile.

addObjectFile calls RuntimeDyld::loadObject.
RuntimeDld::loadObject calls RuntimeDyldELF::createObjectFromFile

And the pointer is never owned at this point. I say this point, because
the alternative codepath, RuntimeDyldMachO::createObjectFile certainly
does take ownership, so this seemed like a good hint that this was a/the
right place to take ownership.