[lldb] expr is broken (also affects print)
expr command hasn't been updated to deal with capabilities. In addition, it causes mayhem in the debugging session by modifying the top bits and tags of (some) capability registers . This is because
expr needs to save and restore all the registers before executing the expression, but at the moment we do not have support in ptrace to write capability registers. Therefore, only the 64-bit registers are restored.
While ptrace support is missing, we should at least disable
expr to avoid causing confusion for the users. We could also update
frame var if we can detect that the argument is a single identifier.