rand_unix.c: correct include guard comments

Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10050)

(cherry picked from commit 2a7e6ed86be20bd472696a3eafe5d20ec9579dab)

crypto/rand/rand_unix.c

@@ -80,7 +80,8 @@ static uint64_t get_timer_bits(void);
 #   define OSSL_POSIX_TIMER_OKAY
 #  endif
 # endif
-#endif /* defined(OPENSSL_SYS_UNIX) || defined(__DJGPP__) */
+#endif /* (defined(OPENSSL_SYS_UNIX) && !defined(OPENSSL_SYS_VXWORKS))
+          || defined(__DJGPP__) */
 
 #if defined(OPENSSL_RAND_SEED_NONE)
 /* none means none. this simplifies the following logic */
@@ -860,4 +861,5 @@ static uint64_t get_timer_bits(void)
 # endif
     return time(NULL);
 }
-#endif /* defined(OPENSSL_SYS_UNIX) || defined(__DJGPP__) */
+#endif /* (defined(OPENSSL_SYS_UNIX) && !defined(OPENSSL_SYS_VXWORKS))
+          || defined(__DJGPP__) */