Improve macro definition in order to avoid potential precedence issues.

For example, sparse spotted that the following line was spurious:
        newcond->flags &= ~CONDFLAG_NOCASE;
It this particular case, 2 bits were resetted (instead of only 1). This was harmless because the first bit (i.e. CONDFLAG_NONE) is never tested as-is.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1701545 13f79535-47bb-0310-9956-ffa450edef68