objc-mode: Fix exceptions in fontification.

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.