fix random build error with -no-feature-commandlineparser

when the dbus tools are bootstrapped (which is the case in x-builds and
when above feature is disabled), they are built asynchronously to the
corelib module. but as qdbusxml2cpp's project file needs to check the
need for bootstrapping, it needs corelib's configuration. so pull it in
explicitly.

Change-Id: I559c7590a3eba8d3f8a03c44fe3a6d56f1c56db0
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

src/tools/qdbusxml2cpp/qdbusxml2cpp.pro

@@ -1,6 +1,9 @@
 option(host_build)
-!force_bootstrap:!qtConfig(commandlineparser): \
-    CONFIG += force_bootstrap
+!force_bootstrap {
+    include($$OUT_PWD/../../corelib/qtcore-config.pri)
+    !qtConfig(commandlineparser): \
+        CONFIG += force_bootstrap
+}
 QT = core-private
 force_bootstrap: QT += bootstrap_dbus-private
 else: QT += dbus-private