Fix domain events C example on Win32

printf on Win32 does not necessarily support %lld and we don't
have GNULIBs wrapper for printf(). Switch to use asprintf() for
which we do have a gnulib wrapper with %lld support

* examples/domain-events/events-c/event-test.c: Fix formatting
  of %lld on Win32
* cfg.mk: Don't require use of virAsprintf since this is an
  example app for out of tree users to follow

cfg.mk

@@ -571,7 +571,7 @@ exclude_file_name_regexp--sc_prohibit_always_true_header_tests = \
   (^docs|^python/(libvirt-override|typewrappers)\.c$$)
 
 exclude_file_name_regexp--sc_prohibit_asprintf = \
-  ^(bootstrap.conf$$|po/|src/util/util\.c$$)
+  ^(bootstrap.conf$$|po/|src/util/util\.c$$|examples/domain-events/events-c/event-test\.c$$)
 
 exclude_file_name_regexp--sc_prohibit_close = \
   (\.py$$|^docs/|(src/util/files\.c|src/libvirt\.c)$$)

examples/domain-events/events-c/event-test.c

@@ -169,8 +169,16 @@ static int myDomainEventRTCChangeCallback(virConnectPtr conn ATTRIBUTE_UNUSED,
                                           long long offset,
                                           void *opaque ATTRIBUTE_UNUSED)
 {
-    printf("%s EVENT: Domain %s(%d) rtc change %lld\n", __func__, virDomainGetName(dom),
-           virDomainGetID(dom), offset);
+    char *str = NULL;
+    /* HACK: use asprintf since we have gnulib's wrapper for %lld on Win32
+     * but don't have a printf() replacement with %lld */
+    if (asprintf(&str, "%s EVENT: Domain %s(%d) rtc change %lld\n",
+                 __func__, virDomainGetName(dom),
+                 virDomainGetID(dom), offset) < 0)
+        return 0;
+
+    printf("%s", str);
+    free(str);
 
     return 0;
 }