Add the CTX parameter back to EC_GROUP_cmp.

It was a mistake to remove this in the first place.

Change-Id: Icd97b4db01e49151daa41dd892f9da573ddc2842
Reviewed-on: https://boringssl-review.googlesource.com/3541
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/ec/ec.c b/crypto/ec/ec.c
index 30f9346..21a3940 100644
--- a/crypto/ec/ec.c
+++ b/crypto/ec/ec.c
@@ -499,7 +499,7 @@
   }
 }
 
-int EC_GROUP_cmp(const EC_GROUP *a, const EC_GROUP *b) {
+int EC_GROUP_cmp(const EC_GROUP *a, const EC_GROUP *b, BN_CTX *ignored) {
   if (a->curve_name == NID_undef || b->curve_name == NID_undef) {
     return 0;
   }
diff --git a/crypto/evp/p_ec_asn1.c b/crypto/evp/p_ec_asn1.c
index d2d6792..8967b50 100644
--- a/crypto/evp/p_ec_asn1.c
+++ b/crypto/evp/p_ec_asn1.c
@@ -382,7 +382,7 @@
 static int ec_cmp_parameters(const EVP_PKEY *a, const EVP_PKEY *b) {
   const EC_GROUP *group_a = EC_KEY_get0_group(a->pkey.ec),
                  *group_b = EC_KEY_get0_group(b->pkey.ec);
-  return EC_GROUP_cmp(group_a, group_b);
+  return EC_GROUP_cmp(group_a, group_b, NULL);
 }
 
 static void int_ec_free(EVP_PKEY *pkey) { EC_KEY_free(pkey->pkey.ec); }
diff --git a/include/openssl/ec.h b/include/openssl/ec.h
index 73bfc41..c952d9a 100644
--- a/include/openssl/ec.h
+++ b/include/openssl/ec.h
@@ -117,7 +117,8 @@
 
 /* EC_GROUP_cmp returns one if |a| and |b| are the same group and zero
  * otherwise. */
-OPENSSL_EXPORT int EC_GROUP_cmp(const EC_GROUP *a, const EC_GROUP *b);
+OPENSSL_EXPORT int EC_GROUP_cmp(const EC_GROUP *a, const EC_GROUP *b,
+                                BN_CTX *ignored);
 
 /* EC_GROUP_get0_generator returns a pointer to the internal |EC_POINT| object
  * in |group| that specifies the generator for the group. */