message: Make bench_internal obey secp256k1_fe_sqrt's contract wrt aliasing.
  Summary:
  Bench_internal was previously incorrect but wasn't detected by
  -DVERIFY until PR
  This is a backport of secp256k1's PR591
  Test Plan:
  cmake -GNinja .. -DCMAKE_C_FLAGS=-DVERIFY
  ninja bench-secp256k1-internal
  Reviewers: #bitcoin_abc, Fabien
diff: @@ -184,9 +184,11 @@ void bench_field_inverse_var(void* arg) {
  void bench_field_sqrt(void* arg) {
  int i;
  bench_inv *data = (bench_inv*)arg;
  + secp256k1_fe t;
  for (i = 0; i < 20000; i++) {
  - secp256k1_fe_sqrt(&data->fe_x, &data->fe_x);
  + t = data->fe_x;
  + secp256k1_fe_sqrt(&data->fe_x, &t);
  secp256k1_fe_add(&data->fe_x, &data->fe_y);
  }
  }
  