drm/virgl: add extern C guard for the UAPI header

Cc: Dave Airlie <airlied@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>

include/uapi/drm/virtgpu_drm.h

@@ -26,6 +26,10 @@
 
 #include "drm.h"
 
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 /* Please note that modifications to all structs defined here are
  * subject to backwards-compatibility constraints.
  *
@@ -163,4 +167,8 @@ struct drm_virtgpu_get_caps {
 	DRM_IOWR(DRM_COMMAND_BASE + DRM_VIRTGPU_GET_CAPS, \
 	struct drm_virtgpu_get_caps)
 
+#if defined(__cplusplus)
+}
+#endif
+
 #endif