Remove run-time dependencies on GTK3 backends for Wayland, Mir, Broadway

This allows running with a GTK+ library that was built with different backends
than the one wxWidgets was built with. Since GTK3 provides no way to determine
the backends available at run-time, avoid referencing symbols in the backends
by checking the type name of the GdkDisplay, on the assumption that they are
unlikely to ever be changed. The X11 backend is still required at run-time if
it was available at build-time, although this dependency could also be removed.

src/gtk/toplevel.cpp

@@ -38,20 +38,6 @@
     #include <X11/Xatom.h>  // XA_CARDINAL
     #include "wx/unix/utilsx11.h"
 #endif
-#ifdef GDK_WINDOWING_WAYLAND
-    #include <gdk/gdkwayland.h>
-    #define HAS_CLIENT_DECOR
-#endif
-#ifdef GDK_WINDOWING_MIR
-    extern "C" {
-    #include <gdk/gdkmir.h>
-    }
-    #define HAS_CLIENT_DECOR
-#endif
-#ifdef GDK_WINDOWING_BROADWAY
-    #include <gdk/gdkbroadway.h>
-    #define HAS_CLIENT_DECOR
-#endif
 
 #include "wx/gtk/private.h"
 #include "wx/gtk/private/gtk2-compat.h"
@@ -80,25 +66,29 @@ static enum {
 static bool gs_decorCacheValid;
 #endif
 
-#ifdef HAS_CLIENT_DECOR
+#ifdef __WXGTK3__
 static bool HasClientDecor(GtkWidget* widget)
 {
-    GdkDisplay* display = gtk_widget_get_display(widget);
+    static bool has;
-#ifdef GDK_WINDOWING_WAYLAND
+    static bool once;
-    if (GDK_IS_WAYLAND_DISPLAY(display))
+    if (!once)
-        return true;
+    {
-#endif
+        once = true;
-#ifdef GDK_WINDOWING_MIR
+        GdkDisplay* display = gtk_widget_get_display(widget);
-    if (GDK_IS_MIR_DISPLAY(display))
+        const char* name = g_type_name(G_TYPE_FROM_INSTANCE(display));
-        return true;
+        has =
-#endif
+            strcmp(name, "GdkWaylandDisplay") == 0 ||
-#ifdef GDK_WINDOWING_BROADWAY
+            strcmp(name, "GdkMirDisplay") == 0 ||
-    if (GDK_IS_BROADWAY_DISPLAY(display))
+            strcmp(name, "GdkBroadwayDisplay") == 0;
-        return true;
+    }
-#endif
+    return has;
+}
+#else
+static inline bool HasClientDecor(GtkWidget*)
+{
     return false;
 }
-#endif // HAS_CLIENT_DECOR
+#endif
 
 //-----------------------------------------------------------------------------
 // RequestUserAttention related functions
@@ -253,7 +243,6 @@ size_allocate(GtkWidget*, GtkAllocation* alloc, wxTopLevelWindowGTK* win)
         GtkAllocation a;
         gtk_widget_get_allocation(win->m_widget, &a);
         wxSize size(a.width, a.height);
-#ifdef HAS_CLIENT_DECOR
         if (HasClientDecor(win->m_widget))
         {
             GtkAllocation a2;
@@ -266,7 +255,6 @@ size_allocate(GtkWidget*, GtkAllocation* alloc, wxTopLevelWindowGTK* win)
             win->GTKUpdateDecorSize(decorSize);
         }
         else
-#endif
         {
             size.x += win->m_decorSize.left + win->m_decorSize.right;
             size.y += win->m_decorSize.top + win->m_decorSize.bottom;
@@ -740,9 +728,9 @@ bool wxTopLevelWindowGTK::Create( wxWindow *parent,
 
         if ( style & wxCAPTION )
             m_gdkDecor |= GDK_DECOR_TITLE;
-#if defined(GDK_WINDOWING_WAYLAND) && GTK_CHECK_VERSION(3,10,0)
+#if GTK_CHECK_VERSION(3,10,0)
         else if (
-            GDK_IS_WAYLAND_DISPLAY(gtk_widget_get_display(m_widget)) &&
+            strcmp("GdkWaylandDisplay", g_type_name(G_TYPE_FROM_INSTANCE(gtk_widget_get_display(m_widget)))) == 0 &&
             gtk_check_version(3,10,0) == NULL)
         {
             gtk_window_set_titlebar(GTK_WINDOW(m_widget), gtk_header_bar_new());
@@ -1080,9 +1068,7 @@ void wxTopLevelWindowGTK::DoMoveWindow(int WXUNUSED(x), int WXUNUSED(y), int WXU
 void wxTopLevelWindowGTK::GTKDoGetSize(int *width, int *height) const
 {
     wxSize size(m_width, m_height);
-#ifdef HAS_CLIENT_DECOR
     if (!HasClientDecor(m_widget))
-#endif
     {
         size.x -= m_decorSize.left + m_decorSize.right;
         size.y -= m_decorSize.top + m_decorSize.bottom;
@@ -1239,14 +1225,12 @@ void wxTopLevelWindowGTK::DoSetSizeHints( int minW, int minH,
     hints.max_height = INT_MAX / 16;
     int decorSize_x;
     int decorSize_y;
-#ifdef HAS_CLIENT_DECOR
     if (HasClientDecor(m_widget))
     {
         decorSize_x = 0;
         decorSize_y = 0;
     }
     else
-#endif
     {
         decorSize_x = m_decorSize.left + m_decorSize.right;
         decorSize_y = m_decorSize.top + m_decorSize.bottom;
@@ -1282,13 +1266,11 @@ void wxTopLevelWindowGTK::GTKUpdateDecorSize(const DecorSize& decorSize)
     if (!IsMaximized() && !IsFullScreen())
         GetCachedDecorSize() = decorSize;
 
-#ifdef HAS_CLIENT_DECOR
     if (HasClientDecor(m_widget))
     {
         m_decorSize = decorSize;
         return;
     }
-#endif
 #ifdef GDK_WINDOWING_X11
     if (m_updateDecorSize && memcmp(&m_decorSize, &decorSize, sizeof(DecorSize)))
     {