Use FindInotify.cmake to decide wheter inotify is available.
Summary:
FreeBSD also has sys/inotify.h available, but it is a library.
We added FindInotify.cmake to ecm a while a go for this, but never got
around to upstream the rest of the patches.
Reviewers: FreeBSD, dfaure, kfunk
Reviewed By: kfunk
Subscribers: Frameworks
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D6253