objc-mode: Fix exceptions in fontification.

These exceptions ("Invalid search bound (wrong side of point)")
were observed in test suite file class-24.m when moving point
up and down a line at a time.

* lisp/progmodes/cc-engine.el (c-forward-declarator): In the
c-syntactic-re-search-forward ~30 lines from the end of the
function amend the regexp for objc-mode such that "@end"
terminates the search, but "<" doesn't.

* lisp/progmodes/cc-fonts.el
(c-make-font-lock-search-function): supply a non-nil
CHECK-POINT argument to c-make-font-lock-search-form.

lisp/progmodes/cc-engine.el

@@ -10219,7 +10219,11 @@ point unchanged and return nil."
 			       (prog1
 				   (setq found
 					 (c-syntactic-re-search-forward
-					  "[;:,]\\|\\(=\\|\\s(\\)"
+					  ;; Consider making the next regexp a
+					  ;; c-lang-defvar (2023-07-04).
+					  (if (c-major-mode-is 'objc-mode)
+					      "\\(?:@end\\)\\|[;:,]\\|\\(=\\|[[(]\\)"
+					    "[;:,]\\|\\(=\\|\\s(\\)")
 					  limit 'limit t))
 				 (setq got-init
 				       (and found (match-beginning 1))))

lisp/progmodes/cc-fonts.el

@@ -387,7 +387,7 @@
 	      (parse-sexp-lookup-properties
 	       (cc-eval-when-compile
 		 (boundp 'parse-sexp-lookup-properties))))
-	  ,(c-make-font-lock-search-form regexp highlights))
+	  ,(c-make-font-lock-search-form regexp highlights t))
 	nil)))
 
   (defun c-make-font-lock-BO-decl-search-function (regexp &rest highlights)