basic/missing_*.h: add asserts that the values are as expected

It's great that we provide fallback values, but if we got one of those wrong,
it could be a long time before anyone noticed. So let's add asserts that the
our internal defines actually match the official ones, when the latter are
available.

I did not add '#include "macro.h"' to missing_{audit,capability}, because
those are processed by an awk script that would need additional include
directories and could be confused by the additional lines. We don't include
those headers standalone anyway, so this is not necessary anyway.

src/basic/missing_audit.h

@@ -4,21 +4,29 @@
 #include <linux/audit.h>
 
 #if HAVE_AUDIT
-#include <libaudit.h>
+#  include <libaudit.h>
 #endif
 
 #ifndef AUDIT_SERVICE_START
-#define AUDIT_SERVICE_START 1130 /* Service (daemon) start */
+#  define AUDIT_SERVICE_START 1130 /* Service (daemon) start */
+#else
+assert_cc(AUDIT_SERVICE_START == 1130);
 #endif
 
 #ifndef AUDIT_SERVICE_STOP
-#define AUDIT_SERVICE_STOP 1131 /* Service (daemon) stop */
+#  define AUDIT_SERVICE_STOP 1131 /* Service (daemon) stop */
+#else
+assert_cc(AUDIT_SERVICE_STOP == 1131);
 #endif
 
 #ifndef MAX_AUDIT_MESSAGE_LENGTH
-#define MAX_AUDIT_MESSAGE_LENGTH 8970
+#  define MAX_AUDIT_MESSAGE_LENGTH 8970
+#else
+assert_cc(MAX_AUDIT_MESSAGE_LENGTH == 8970);
 #endif
 
 #ifndef AUDIT_NLGRP_MAX
-#define AUDIT_NLGRP_READLOG 1
+#  define AUDIT_NLGRP_READLOG 1
+#else
+assert_cc(AUDIT_NLGRP_READLOG == 1);
 #endif