tools: Move ARRAY_SIZE() into xen-tools/libs.h

xen-tools/libs.h currently contains a shared BUILD_BUG_ON() implementation and
is used by some tools.  Extend this to include ARRAY_SIZE and clean up all the
opencoding.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

tools/python/xen/lowlevel/xc/xc.c

@@ -22,7 +22,7 @@
 #include <xen/hvm/hvm_info_table.h>
 #include <xen/hvm/params.h>
 
-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#include <xen-tools/libs.h>
 
 /* Needed for Python versions earlier than 2.3. */
 #ifndef PyMODINIT_FUNC