Fix some linkage errors

Author: oskirby

linux/debian/control

@@ -64,7 +64,6 @@ Vcs-Git: https://github.com/mozilla-mobile/mozilla-vpn-client
 Package: mozillavpn
 Architecture: any
 Depends: wireguard (>=1.0.20200319),
-         wireguard-tools (>=1.0.20200319),
          libfreetype6,
          libfontconfig1,
          libegl1,

src/cmake/linux.cmake

@@ -50,6 +50,7 @@ if(NOT BUILD_FLATPAK)
     # Link to polkit
     find_package(PkgConfig REQUIRED)
     pkg_check_modules(polkit REQUIRED IMPORTED_TARGET polkit-gobject-1)
+    target_link_libraries(mozillavpn PRIVATE PkgConfig::polkit)
 
     if (QT_FEATURE_static)
         find_package(Qt6 REQUIRED COMPONENTS WaylandClientPrivate)
@@ -58,7 +59,10 @@ if(NOT BUILD_FLATPAK)
         target_link_libraries(mozillavpn PRIVATE Qt6::WaylandClientPrivate)
     endif()
 
-    target_link_libraries(mozillavpn PRIVATE PkgConfig::polkit)
+    # Add the offscreen backend support when building for debug.
+    if (QT_FEATURE_static AND CMAKE_BUILD_TYPE STREQUAL "Debug")
+        qt_import_plugins(mozillavpn INCLUDE Qt6::QOffscreenIntegrationPlugin)
+    endif()
 
     target_sources(mozillavpn PRIVATE
         ${CMAKE_SOURCE_DIR}/src/platforms/linux/linuxcontroller.cpp