PR12427 introduced the ability to let a user abbreviate process
probes by inferring the path from the -c CMD argument.  We can do
the same with -x PID, perhaps the following way:

- stap --no-use-server -e 'probe process.foo {}' -x PID
  .... map to process("PATH") where PATH = readlink("/proc/PID/exe"),
  in the same place as PR12427 (dwarf_builder::build)

- stap --use-server -e 'probe process.foo {}' -x PID
  .... map to stap server_options "-c PATH" with same PATH
  (IOW, pretend to the stap-server that the user typed -c PATH).