Fix a cacheing bug, which led to inordinately slow c-beginning-of-defun.
* lisp/progmodes/cc-defs.el (c-self-bind-state-cache): New macro.
* lisp/progmodes/cc-engine.el (c-ssb-lit-begin): Always call c-parse-state
rather than just using the cache variable c-state-cache.
(c-syntactic-skip-backward): Invoke c-self-bind-state-cache to isolate calls
to c-parse-state from other uses of the parse state cache.
* lisp/progmodes/cc-cmds.el (c-beginning-of-defun, c-end-of-defun): Invoke
c-self-bind-state-cache around the processing, replacing flawed bindings of
c-state-cache.