Make major mode work with cc-mode-5.30+.

Make major mode work with cc-mode-5.30+.
(antlr-c-init-language-vars): New function.
(antlr-mode): Use it with cc-mode before v5.29.
(antlr-c-common-init): Don't set some local vars here.
(antlr-mode): Set them here.
(antlr-c-forward-sws): New function alias.
(antlr-mode): Redefine with cc-mode before v5.30.
(antlr-skip-sexps): Use it.
(antlr-skip-exception-part): Ditto.
(antlr-skip-file-prelude): Ditto.
(antlr-outside-rule-p): Ditto.
(antlr-end-of-body): Ditto.
(antlr-option-kind): Ditto.
(antlr-insert-option-area): Ditto.
(antlr-file-dependencies): Ditto.