Toggle the display of GUD tooltips.
With a prefix argument ARG, enable the feature if ARG is
positive, and disable it otherwise. If called from Lisp, enable
it if ARG is omitted or nil.
(fn &optional ARG)
Non-nil if Gud-Tooltip mode is enabled.
See the command `gud-tooltip-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `gud-tooltip-mode'.