Added unistd.h missing from CWaylandOutputViewport

Signed-off-by: Alexis Maiquez <almamu@almamu.com>

src/WallpaperEngine/Render/Drivers/Output/CWaylandOutputViewport.cpp

@@ -13,6 +13,8 @@ extern "C" {
 #undef namespace
 #undef static
 
+#include <unistd.h>
+
 using namespace WallpaperEngine::Render::Drivers;
 using namespace WallpaperEngine::Render::Drivers::Output;