fix build problem on platforms without atomic instructions

Thanks to Michael Biebl for his very helpful analysis of the bug.
bugfix: in 7.6.4, pri-based filters did not work correctly

messages were distributed to the wrong bins.
prepare for 7.6.5 release
Merge branch 'v7-stable' of git+ssh://git.adiscon.com/git/rsyslog into v7-stable