Fix -Wundef warnings for patterns `#if HAVE`

* See [Feature #17752]
* Using this to detect them:
  git grep -P 'if\s+HAVE' | grep -Pv 'HAVE_LONG_LONG|/ChangeLog|HAVE_TYPEOF'

1 files changed, 1 insertions, 1 deletions

diff --git a/random.c b/random.c
index eec017cfd5..2c9fe0c906 100644
--- a/random.c
+++ b/random.c
@@ -428,7 +428,7 @@ random_init(int argc, VALUE *argv, VALUE obj)
 # define USE_DEV_URANDOM 0
 #endif
 
-#if HAVE_GETENTROPY
+#ifdef HAVE_GETENTROPY
 # define MAX_SEED_LEN_PER_READ 256
 static int
 fill_random_bytes_urandom(void *seed, size_t size)