meson: -display dbus and CFI are incompatible

The generated skeletons for DBus call the finalize method of the parent
type using code like

    G_OBJECT_CLASS (qemu_dbus_display1_chardev_skeleton_parent_class)->finalize (object);

However, the finalize method is defined in a shared library that is not
compiled with CFI.  Do not enable anything that uses gdbus-codegen if
--enable-cfi was specified.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

meson.build

@@ -487,6 +487,7 @@ meson.override_dependency('glib-2.0', glib)
 
 gio = not_found
 gdbus_codegen = not_found
+gdbus_codegen_error = '@0@ requires gdbus-codegen, please install libgio'
 if not get_option('gio').auto() or have_system
   gio = dependency('gio-2.0', required: get_option('gio'),
                    method: 'pkg-config', kwargs: static_kwargs)
@@ -511,6 +512,10 @@ if not get_option('gio').auto() or have_system
                              version: gio.version())
   endif
 endif
+if gdbus_codegen.found() and get_option('cfi')
+  gdbus_codegen = not_found
+  gdbus_codegen_error = '@0@ uses gdbus-codegen, which does not support control flow integrity'
+endif
 
 lttng = not_found
 if 'ust' in get_option('trace_backends')
@@ -1676,7 +1681,7 @@ dbus_display = get_option('dbus_display') \
   .require(enable_modules,
            error_message: '-display dbus requires --enable-modules') \
   .require(gdbus_codegen.found(),
-           error_message: '-display dbus requires gdbus-codegen') \
+           error_message: gdbus_codegen_error.format('-display dbus')) \
   .require(opengl.found() and gbm.found(),
            error_message: '-display dbus requires epoxy/egl and gbm') \
   .allowed()