* progmodes/gud.el (gud-stop-subjob, gud-menu-map): Respect GDB

* progmodes/gud.el (gud-stop-subjob, gud-menu-map): Respect GDB
non-stop settings.

* progmodes/gdb-mi.el (gdb-thread-number): Initialize with nil.
(gdb-current-context-command): Do not append --thread if
`gdb-thread-number' is nil.
(gdb-running-threads-count, gdb-stopped-threads-count): New
variables.
(gdb-non-stop, gdb-gud-control-all-threads, gdb-switch-reasons)
(gdb-stopped-hooks, gdb-switch-when-another-stopped): New
customization options.
(gdb-gud-context-command, gdb-gud-context-call): New wrappers for
GUD commands.
(gdb): `gud-def' definitions changed to use `gdb-gud-context-call'
(gdb-init-1): Activate non-stop mode if `gdb-non-stop' is enabled.
(gdb-setq-thread-number, gdb-update-gud-running): New functions to
set `gdb-thread-number' and update `gud-running' properly.
(gdb-running): Update threads list when new threads appear.
(gdb-stopped): Support non-stop operation and new thread switching
logic.
(gdb-jsonify-buffer, gdb-json-read-buffer, gdb-json-string)
(gdb-json-partial-output): New set of JSON routines.
(def-gdb-auto-update-trigger): New `signal-list' optional
argument.
(gdb-thread-list-handler-custom): Update `gud-running',
`gdb-stopped-threads-count' and `gdb-running-threads-count'.
(def-gdb-thread-buffer-gdb-command, gdb-interrupt-thread)
(gdb-continue-thread, gdb-step-thread): New commands for fine
thread execution control.
(gud-menu-map): New menu items to switch non-stop options.
(gdb-reset): Cleanup `gdb-thread-position' overlay arrow marker.