gdb: add destructor to lwp_info

Replace the lwp_free function with a destructor.  Make lwp_info
non-copyable, since there is now a destructor (we wouldn't want an
lwp_info object getting copied and this->arch_private getting deleted
twice).

Change-Id: I09fcbe967e362566d3a06fed2abca2a9955570fa
2 files changed