c-syntactic-skip-backward is a compiled Lisp function in `cc-engine.el'.

(c-syntactic-skip-backward SKIP-CHARS &optional LIMIT PAREN-LEVEL)

Like `skip-chars-backward' but only look at syntactically relevant chars,
i.e. don't stop at positions inside syntactic whitespace or string
literals. Preprocessor directives are also ignored, with the exception
of the one that the point starts within, if any. If LIMIT is given,
it's assumed to be at a syntactically relevant position.

If PAREN-LEVEL is non-nil, the function won't stop in nested paren
sexps, and the search will also not go outside the current paren sexp.
However, if LIMIT or the buffer limit is reached inside a nested paren
then the point will be left at the limit.

Non-nil is returned if the point moved, nil otherwise.

Note that this function might do hidden buffer changes. See the
comment at the start of cc-engine.el for more info.