Small Stack ECC Pairwise Consistency Test

1. Update the ECC PCT to use the key's heap to allocate any buffers for
   the test. This is similar to how RSA does it.
2. Put the buffers on the stack if not using small stack option.

wolfcrypt/src/ecc.c

@@ -10211,23 +10211,31 @@ static int _ecc_pairwise_consistency_test(ecc_key* key, WC_RNG* rng)
     }
 
     if (!err && (flags & WC_ECC_FLAG_DEC_SIGN)) {
+#ifndef WOLFSSL_SMALL_STACK
+        byte sig[MAX_ECC_BYTES + WC_SHA256_DIGEST_SIZE];
+#else
         byte* sig;
+#endif
         byte* digest;
         word32 sigLen, digestLen;
         int dynRng = 0, res = 0;
 
         sigLen = (word32)wc_ecc_sig_size(key);
         digestLen = WC_SHA256_DIGEST_SIZE;
-        sig = (byte*)XMALLOC(sigLen + digestLen, NULL, DYNAMIC_TYPE_ECC);
+#ifdef WOLFSSL_SMALL_STACK
+        sig = (byte*)XMALLOC(sigLen + digestLen, key->heap, DYNAMIC_TYPE_ECC);
         if (sig == NULL)
             return MEMORY_E;
+#endif
         digest = sig + sigLen;
 
         if (rng == NULL) {
             dynRng = 1;
-            rng = wc_rng_new(NULL, 0, NULL);
+            rng = wc_rng_new(NULL, 0, key->heap);
             if (rng == NULL) {
-                XFREE(sig, NULL, DYNAMIC_TYPE_ECC);
+#ifdef WOLFSSL_SMALL_STACK
+                XFREE(sig, key->heap, DYNAMIC_TYPE_ECC);
+#endif
                 return MEMORY_E;
             }
         }
@@ -10248,7 +10256,9 @@ static int _ecc_pairwise_consistency_test(ecc_key* key, WC_RNG* rng)
             wc_rng_free(rng);
         }
         ForceZero(sig, sigLen + digestLen);
-        XFREE(sig, NULL, DYNAMIC_TYPE_ECC);
+#ifdef WOLFSSL_SMALL_STACK
+        XFREE(sig, key->heap, DYNAMIC_TYPE_ECC);
+#endif
     }
     (void)rng;