[lldb] [llgs] Include process id in W/X stop reasons

Include the process identifier in W/X stop reasons when multiprocess
extensions are enabled.

The LLDB client does not support process identifiers there at the moment
but it parses packets in such a way that their presence does not cause
any problems.

Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.llvm.org/D127191