Disable DBus (and X11) on Windows/macOS/Android per default

Like Kate, one should not try to use DBus on platform that not
support it. At the moment we have hacks in the Craft blueprints
to avoid the worst, but not using it is much nicer.

If the user wants to compile it, we have a USE_DBUS CMake option.

CMakeLists.txt

@@ -45,7 +45,6 @@ include(ECMEnableSanitizers)
 
 find_package(Qt6 ${QT_MIN_VERSION} CONFIG REQUIRED
     Core
-    DBus
     Multimedia
     PrintSupport
     Widgets
@@ -59,7 +58,6 @@ find_package(KF6 ${KF6_DEP_VERSION} REQUIRED
     CoreAddons
     Crash
     GuiAddons
-    DBusAddons
     I18n
     IconThemes
     KIO
@@ -80,10 +78,22 @@ if (NOT WIN32)
     )
 endif()
 
-if (NOT WIN32 AND NOT APPLE)
+# shall we use DBus?
+# enabled per default on Linux & BSD systems
+set(USE_DBUS_DEFAULT OFF)
+if(UNIX AND NOT APPLE AND NOT ANDROID AND NOT HAIKU)
+    set(USE_DBUS_DEFAULT ON)
+endif()
+option(USE_DBUS "Build components using DBus" ${USE_DBUS_DEFAULT})
+if(USE_DBUS)
+    find_package(Qt6 ${QT_MIN_VERSION} CONFIG REQUIRED
+        DBus
+    )
     find_package(KF6 ${KF6_DEP_VERSION} REQUIRED
+        DBusAddons
         GlobalAccel
     )
+    set(HAVE_DBUS 1)
 endif()
 
 find_package(KF6DocTools ${KF6_DEP_VERSION})
@@ -94,7 +104,7 @@ set_package_properties(KF6DocTools PROPERTIES DESCRIPTION
 
 find_package(ICU 61.0 COMPONENTS uc i18n REQUIRED)
 
-if(NOT APPLE)
+if(UNIX AND NOT APPLE AND NOT ANDROID AND NOT HAIKU)
     option(WITHOUT_X11 "Build without X11 integration (skips finding X11)" OFF)
     if (NOT WITHOUT_X11)
         find_package(X11)
@@ -130,7 +140,7 @@ add_subdirectory( src )
 add_subdirectory( data )
 add_subdirectory( desktop )
 
-if (NOT WIN32 AND NOT APPLE)
+if (HAVE_DBUS)
     add_subdirectory( kconf_update )
 endif()