Added ATTR_PURE macro, which expands to pure attribute if available.
Added ATTR_PURE macro, which expands to pure attribute if available.

--HG--
branch : HEAD

jkerihuel/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,jkerihuel/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,jwm/dovecot-notmuch,jkerihuel/dovecot