Fix the compilation of kiten on Windows

Summary:
This patch :
* fixes the export behavior on Windows by using the cmake GenerateExportHeader feature
* allows research and inclusion of mman.h/mman.lib

Test Plan:
Tested on windows/neon

{F6314461}

Reviewers: #kde_edu, kfunk

Reviewed By: kfunk

Subscribers: kfunk, kde-edu

Tags: #kde_edu, #windows

Differential Revision: https://phabricator.kde.org/D16061