gdb/infrun: add reason parameter to stop_all_threads

Add a "reason" parameter, only used to show in debug messages what is
the reason for stopping all threads.  This helped me understand the
debug logs while adding some new uses of stop_all_threads, so I am
proposing to merge it.

Change-Id: I66c8c335ebf41836a7bc3d5fe1db92c195f65e55
4 files changed