message: secp256k1_fe_sqrt: Verify that the arguments don't alias.
  Summary: This is a backport of secp256k1's PR551
  Test Plan:
  ninja check-secp256k1
  Reviewers: #bitcoin_abc, Fabien
  Subscribers: Fabien
diff: @@ -48,6 +48,8 @@ static int secp256k1_fe_sqrt(secp256k1_fe *r, const secp256k1_fe *a) {
  secp256k1_fe x2, x3, x6, x9, x11, x22, x44, x88, x176, x220, x223, t1;
  int j;
  + VERIFY_CHECK(r != a);
  +
  /** The binary representation of (p + 1)/4 has 3 blocks of 1s, with lengths in
  * { 2, 22, 223 }. Use an addition chain to calculate 2^n - 1 for each block:
  * 1, [2], 3, 6, 9, 11, [22], 44, 88, 176, 220, [223]
  