Silence an uninitialized variable false positive in GCC.

When building with OPENSSL_NO_ASM, things are inlined enough that GCC
figures out bn_reduce_once reads words, but not that
bn_big_endian_to_words initializes the parts that are read.

Change-Id: Id4d77cec6ca0782edd0d93022436bd307c2bba17
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/56826
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Bob Beck <bbe@google.com>
Auto-Submit: David Benjamin <davidben@google.com>

crypto/fipsmodule/ec/ec.c

diff --git a/crypto/fipsmodule/ec/ec.c b/crypto/fipsmodule/ec/ec.c
index 4e632e1..debb965 100644
--- a/crypto/fipsmodule/ec/ec.c
+++ b/crypto/fipsmodule/ec/ec.c
@@ -1195,7 +1195,7 @@
   // Additionally, one can manually check this property for built-in curves. It
   // is enforced for legacy custom curves in |EC_GROUP_set_generator|.
   const BIGNUM *order = &group->order;
-  BN_ULONG words[EC_MAX_WORDS + 1];
+  BN_ULONG words[EC_MAX_WORDS + 1] = {0};
   bn_big_endian_to_words(words, order->width + 1, bytes, len);
   bn_reduce_once(out->words, words, /*carry=*/words[order->width], order->d,
                  order->width);