Add libkf5windowsystem-dev to build dependencies.

debian/changelog

@@ -2,6 +2,7 @@ liblxqt (0.14.1-4ubuntu2) UNRELEASED; urgency=medium
 
   * Remove upstream patches fixing Mac OS X and Hurd builds.
   * Run wrap-and-sort.
+  * Add libkf5windowsystem-dev to build dependencies.
 
  -- Simon Quigley <tsimonq2@ubuntu.com>  Thu, 23 Apr 2020 03:19:56 -0500
 

debian/control

@@ -8,6 +8,7 @@ Section: libs
 Priority: optional
 Build-Depends: debhelper-compat (= 12),
                dh-exec,
+               libkf5windowsystem-dev (>= 5.36.0),
                libpolkit-qt5-1-dev,
                libqt5svg5-dev,
                libqt5x11extras5-dev,