[gtk+] wayland: Add support for BTN_STYLUS3

[Carlos Garnacho <carlosg src gnome org>]

commit 6fd6ff2ea10f00ff27a3df638a135f9d7fb02152
Author: Jason Gerecke <killertofu gmail com>
Date:   Tue Oct 10 09:17:43 2017 -0700

    wayland: Add support for BTN_STYLUS3
    
    BTN_STYLUS3 is defined by the Linux 4.15 kernel and is sent when the
    third button on a stylus is pressed. At the moment, only Wacom's "Pro
    Pen 3D" has three stylus buttons. Pressing this button triggers a button
    8 event to be sent under X11, so we use the same mapping here.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=790033

 gdk/wayland/gdkdevice-wayland.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/gdk/wayland/gdkdevice-wayland.c b/gdk/wayland/gdkdevice-wayland.c
index 55cfa89..4dde622 100644
--- a/gdk/wayland/gdkdevice-wayland.c
+++ b/gdk/wayland/gdkdevice-wayland.c
@@ -49,6 +49,10 @@
 
 #define BUTTON_BASE (BTN_LEFT - 1) /* Used to translate to 1-indexed buttons */
 
+#ifndef BTN_STYLUS3
+#define BTN_STYLUS3 0x149 /* Linux 4.15 */
+#endif
+
 typedef struct _GdkWaylandDevicePad GdkWaylandDevicePad;
 typedef struct _GdkWaylandDevicePadClass GdkWaylandDevicePadClass;
 
@@ -3611,6 +3615,8 @@ tablet_tool_handle_button (void                      *data,
     n_button = GDK_BUTTON_SECONDARY;
   else if (button == BTN_STYLUS2)
     n_button = GDK_BUTTON_MIDDLE;
+  else if (button == BTN_STYLUS3)
+    n_button = 8; /* Back */
   else
     return;