Moved helper macro to a discrete include file.

To help reduce code duplication and also 'kitchen-sink' includes
the ARRAY_LENGTH macro was moved to a stand-alone file and
referenced from the sources consuming it. Other macros will be
added in subsequent passes.

Signed-off-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>

xwayland/selection.c

@@ -31,6 +31,7 @@
 #include <fcntl.h>
 
 #include "xwayland.h"
+#include "shared/helpers.h"
 
 static int
 writable_callback(int fd, uint32_t mask, void *data)

xwayland/window-manager.c

@@ -42,6 +42,7 @@
 #include "cairo-util.h"
 #include "compositor.h"
 #include "hash.h"
+#include "shared/helpers.h"
 
 struct wm_size_hints {
 	uint32_t flags;