kde/sddm: port to Qt6 + Wayland-only (fix greeter XCB + XAuth compile errors)

Three fixes to build sddm on Redox (Wayland-only, Qt6):
 - KeyboardModel.cpp: guard the XcbKeyboardBackend include + its runtime branch
   with #ifndef __redox__ (platformName is never 'xcb' on Redox, but the dead
   branch still pulled in <xcb/xkb.h> -> fatal error). Wayland backend kept.
 - XAuth.h: declare ~XAuth() (the recipe's XAuth.cpp defines it, but the header
   only declared the ctor -> 'definition of implicitly-declared destructor').
 - wayland-patch.sh XAuth.cpp heredoc: add <QFileInfo> + <QRandomGenerator>
   includes and replace Qt5 qrand() with QRandomGenerator (removed in Qt6).

local/recipes/kde/sddm/source/src/common/XAuth.h

@@ -30,6 +30,7 @@ class XAuth
 {
 public:
     XAuth();
+    ~XAuth();
 
     QString authDirectory() const;
     void setAuthDirectory(const QString &path);

local/recipes/kde/sddm/source/src/greeter/KeyboardModel.cpp

@@ -23,7 +23,9 @@
 #include "KeyboardModel.h"
 #include "KeyboardModel_p.h"
 #include "waylandkeyboardbackend.h"
+#ifndef __redox__
 #include "XcbKeyboardBackend.h"
+#endif
 
 namespace SDDM {
     /**********************************************/
@@ -31,11 +33,14 @@ namespace SDDM {
     /**********************************************/
 
     KeyboardModel::KeyboardModel() : d(new KeyboardModelPrivate) {
+#ifndef __redox__
         if (QGuiApplication::platformName() == QLatin1String("xcb")) {
             m_backend = new XcbKeyboardBackend(d);
             m_backend->init();
             m_backend->connectEventsDispatcher(this);
-        } else if (QGuiApplication::platformName().contains(QLatin1String("wayland"))) {
+        } else
+#endif
+        if (QGuiApplication::platformName().contains(QLatin1String("wayland"))) {
             m_backend = new WaylandKeyboardBackend(d);
             m_backend->init();
         }

local/recipes/kde/sddm/wayland-patch.sh

@@ -123,6 +123,8 @@ if [ -f "$SRC/src/common/XAuth.cpp" ]; then
 
 #include <QDebug>
 #include <QFile>
+#include <QFileInfo>
+#include <QRandomGenerator>
 #include <QStandardPaths>
 
 #include <fcntl.h>
@@ -209,7 +211,7 @@ bool XAuth::addCookie(const QString &display) {
      * implementation via the xcb / X11 system library. */
     m_cookie = QByteArray(16, '\0');
     for (int i = 0; i < m_cookie.size(); i++) {
-        m_cookie[i] = static_cast<char>(qrand() & 0xFF);
+        m_cookie[i] = static_cast<char>(QRandomGenerator::global()->generate() & 0xFF);
     }
     return true;
 }