Do not build geoclue plugins on platforms != linux

While dbus might be available on other platforms, the plugin might not be
functional and thus should not be built on these.

Change-Id: I7671a3ecaba6944f99317eee4f7738a7df98ba10
Reviewed-by: Andy Shaw <andy.shaw@qt.io>
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

src/plugins/position/position.pro

@@ -2,8 +2,8 @@ TEMPLATE = subdirs
 
 QT_FOR_CONFIG += positioning-private
 
-qtHaveModule(dbus):SUBDIRS += geoclue
-qtHaveModule(dbus):SUBDIRS += geoclue2
+linux:qtHaveModule(dbus):SUBDIRS += geoclue
+linux:qtHaveModule(dbus):SUBDIRS += geoclue2
 qtConfig(gypsy):SUBDIRS += gypsy
 qtConfig(winrt_geolocation):SUBDIRS += winrt
 qtHaveModule(simulator):SUBDIRS += simulator