Add missing cerrno include.

(cherry picked from commit 99b2e6072c544cc1630dcf3b72e062bdf0503d5f)

src/backends/drm/drm_qpainter_layer.cpp

@@ -19,6 +19,7 @@
 #include "drm_qpainter_backend.h"
 #include "drm_virtual_output.h"
 
+#include <cerrno>
 #include <drm_fourcc.h>
 
 namespace KWin

src/backends/x11/windowed/x11_windowed_qpainter_backend.cpp

@@ -11,6 +11,7 @@
 #include "x11_windowed_logging.h"
 #include "x11_windowed_output.h"
 
+#include <cerrno>
 #include <string.h>
 #include <sys/shm.h>
 #include <xcb/present.h>

src/utils/ramfile.cpp

@@ -13,6 +13,7 @@
 
 #include <QScopeGuard>
 
+#include <cerrno>
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <unistd.h>