Fix linking of the core plugin on Windows.

DestroyIcon needs user32.dll.

Introduced by e0f16c30 .

Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Daniel Molkentin <daniel.molkentin@nokia.com>
(cherry picked from commit 506df46f)

Change-Id: I11075c9cb911af403cb5ded74437c5a785fb768c
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Daniel Molkentin <daniel.molkentin@nokia.com>