xquartz: fix missing include of <errno.h>

It's much cleaner to always include directly what one needs,
instead of relying on very indirect including.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1435>

hw/xquartz/applewm.c

@@ -34,6 +34,8 @@
 #include <dix-config.h>
 #endif
 
+#include <errno.h>
+
 #include "quartz.h"
 
 #include "misc.h"

hw/xquartz/mach-startup/bundle-main.c

@@ -34,6 +34,7 @@
 #include <dix-config.h>
 #endif
 
+#include <errno.h>
 #include <X11/Xlib.h>
 #include <assert.h>
 #include <unistd.h>