Add a fallback definition for __NR_getrandom for ARM linux

Reviewed-by: NPaul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9619)

(cherry picked from commit 24d932ec842bc5fdbd5e9b519cecf15a56bc74e6)

crypto/rand/rand_unix.c

@@ -275,6 +275,13 @@ static ssize_t sysctl_random(char *buf, size_t buflen)
 #  endif
 
 #  if defined(OPENSSL_RAND_SEED_GETRANDOM)
+
+#   if defined(__linux) && !defined(__NR_getrandom)
+#    if defined(__arm__) && defined(__NR_SYSCALL_BASE)
+#     define __NR_getrandom    (__NR_SYSCALL_BASE+384)
+#    endif
+#   endif
+
 /*
  * syscall_random(): Try to get random data using a system call
  * returns the number of bytes returned in buf, or < 0 on error.