libobjc: Fix typos

Fix typos in comments.

libobjc/ChangeLog:

	* Makefile.in: s/overrridden/overridden.
	* encoding.c (_darwin_rs6000_special_round_type_align): Fix typo
	in comment.
	(rs6000_special_round_type_align): Likewise.
	* exception.c (is_kind_of_exception_matcher): Likewise.
	(PERSONALITY_FUNCTION): Likewise.
	* hash.c (objc_hash_next): Likewise.
	* init.c (__objc_create_classes_tree): Likewise.
	* objc-private/objc-list.h (list_remove_head): Likewise.
	* sendmsg.c (__objc_install_dtable_for_class): Likewise.
	* thr.c (objc_thread_yield): Likewise.

Signed-off-by: Andrew Kreimer <algonell@gmail.com>