Auto merge of #2335 - str4d:2333-validation-speed, r=str4d

Switch to libsecp256k1-based validation for ECDSA

Cherry-picked from the following upstream PRs:

- bitcoin/bitcoin#6983
- bitcoin/bitcoin#6954

Part of #2333.

src/gtest/main.cpp

@@ -1,9 +1,17 @@
 #include "gtest/gtest.h"
 #include "crypto/common.h"
+#include "pubkey.h"
 
 #include "libsnark/common/default_types/r1cs_ppzksnark_pp.hpp"
 #include "libsnark/zk_proof_systems/ppzksnark/r1cs_ppzksnark/r1cs_ppzksnark.hpp"
 
+struct ECCryptoClosure
+{
+    ECCVerifyHandle handle;
+};
+
+ECCryptoClosure instance_of_eccryptoclosure;
+
 int main(int argc, char **argv) {
   assert(init_and_check_sodium() != -1);
   libsnark::default_r1cs_ppzksnark_pp::init_public_params();