ui: classic: Include xcb/xcb.h only when X11 is enabled (#1259)

The header may be not available when X11 is disabled. Fixes fcitx5
build without X11 libraries.

Fixes: e723881 ("Clang-tidy clean up for classic ui")

Signed-off-by: Yao Zi <[email protected]>

Author: ziyao233

Diff for: src/ui/classic/classicui.cpp

@@ -20,7 +20,6 @@
 #include <utility>
 #include <vector>
 #include <cairo.h>
-#include <xcb/xcb.h>
 #include "fcitx-config/iniparser.h"
 #include "fcitx-config/rawconfig.h"
 #include "fcitx-utils/color.h"
@@ -45,6 +44,7 @@
 #include "plasmathemewatchdog.h"
 #include "theme.h"
 #ifdef ENABLE_X11
+#include <xcb/xcb.h>
 #include "xcb_public.h"
 #include "xcbui.h"
 #endif