Strange. libapr-1.so.0 contains one or two apr_atomic_xchg* symbols but not apr_atomic_xchgptr. Could you have a foreign apache module installed from somewhere else, from an external package for Ruby perhaps? Do you have any non-OpenSUSE packages or software installed? Or perhaps a hangover from an older version of SUSE?
Hah, ok, a search found the solution. You need to update some additional packages after the update to apache2, which I assume is because you got the latest version during the install.
Starting httpd2 (prefork) /usr/sbin/httpd2-prefork: symbol lookup error: /usr/sbin/httpd2-prefork: undefined symbol: apr_atomic_xchgptr | SUSE & openSUSE