CC Mode: Protect against consecutive calls to before-change-functions ...

CC Mode: Protect against consecutive calls to before-change-functions ...

without an intervening call to after-change-functions.  This would have been a
workaround to bug #38691 had the causes of that bug not been removed.

* lisp/progmodes/cc-mode.el (c-just-done-before-change): Add an extra value to
this variable, 'whole-buffer, this being set by c-before-change as a signal to
c-after-change that although c-before-change has run, it has assumed the
entire buffer as the change region.
(c-before-change, c-after-change): Adapt to the new meaning of the above.