CC Mode: Compensate for backward-sexp ignoring trailing commas after {...}

CC Mode: Compensate for backward-sexp ignoring trailing commas after {...}

This fixes bug #32808.

* lisp/progmodes/cc-engine.el (c-beginning-of-statement-1): New variable
comma-delimited, set when we're about to scan backward over a comma.  Do not
reckon a brace block as bounding a statement when it is followed or preceded
by a comma (except when argument comma-delim is non-nil).
(c-guess-basic-syntax, CASE 9C): Call c-beginning-of-statement-1 with argument
comma-delim changed to non-nil.