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_random.h

@@ -1,6 +1,8 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#include "macro.h"
+
 #if USE_SYS_RANDOM_H
 #  include <sys/random.h>
 #else
@@ -8,13 +10,19 @@
 #endif
 
 #ifndef GRND_NONBLOCK
-#define GRND_NONBLOCK 0x0001
+#  define GRND_NONBLOCK 0x0001
+#else
+assert_cc(GRND_NONBLOCK == 0x0001);
 #endif
 
 #ifndef GRND_RANDOM
-#define GRND_RANDOM 0x0002
+#  define GRND_RANDOM 0x0002
+#else
+assert_cc(GRND_RANDOM == 0x0002);
 #endif
 
 #ifndef GRND_INSECURE
-#define GRND_INSECURE 0x0004
+#  define GRND_INSECURE 0x0004
+#else
+assert_cc(GRND_INSECURE == 0x0004);
 #endif