Add licensing info for libunwind binding, based on convention.

bindings/vapi/libunwind.vapi

@@ -1,6 +1,34 @@
 /*
  * Based on version from Sentry-GLib: https://github.com/arteymix/sentry-glib
  * Courtesy of Guillaume Poirier-Morency <guillaumepoiriermorency@gmail.com>
+ *
+ * Copyright (C) 1996 X Consortium
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy,
+ * modify, merge, publish, distribute, sublicense, and/or sell copies
+ * of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR
+ * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
+ * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * Except as contained in this notice, the name of the X Consortium
+ * shall not be used in advertising or otherwise to promote the sale,
+ * use or other dealings in this Software without prior written
+ * authorization from the X Consortium.
+ *
+ * X Window System is a trademark of X Consortium, Inc.
  */
 
 [CCode (cprefix = "UNW_", lower_case_cprefix = "unw_", cheader_filename = "libunwind.h")]