Use G_N_ELEMENTS() more

In a few places we still use the good old:

  sizeof(var) / sizeof(var[0])
  sizeof(var) / sizeof(int)

The G_N_ELEMENTS() macro is preferred though. In a few places we
don't link with glib, so provide the macro definition.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Kristina Hanicova <khanicov@redhat.com>

examples/c/misc/openauth.c

@@ -7,6 +7,8 @@
 #include <libvirt/libvirt.h>
 #include <libvirt/virterror.h>
 
+#define G_N_ELEMENTS(Array) (sizeof(Array) / sizeof(*(Array)))
+
 static void
 showError(virConnectPtr conn)
 {
@@ -205,7 +207,7 @@ static int credTypes[] = {
 /* The auth struct that will be passed to virConnectOpenAuth */
 static virConnectAuth auth = {
     credTypes,
-    sizeof(credTypes) / sizeof(int),
+    G_N_ELEMENTS(credTypes),
     authCallback,
     NULL, /* cbdata will be initialized in main */
 };