libgcrypt: updated to 1.9.3

Noteworthy changes in version 1.9.3 (2021-04-19)
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* Bug fixes:
  - Fix build problems on i386 using gcc-4.7.
  - Fix checksum calculation in OCB decryption for AES on s390.
  - Fix a regression in gcry_mpi_ec_add related to certain usages of
    curve 25519.
  - Fix a symbol not found problem on Apple M1.
  - Fix for Apple iOS getentropy peculiarity.
  - Make keygrip computation work for compressed points.

* Performance:
  - Add x86_64 VAES/AVX2 accelerated implementation of Camellia.
  - Add x86_64 VAES/AVX2 accelerated implementation of AES.
  - Add VPMSUMD acceleration for GCM mode on PPC.

* Internal changes.
  - Harden MPI conditional code against EM leakage.
  - Harden Elgamal by introducing exponent blinding.
  - Fix memory leaks in the error code paths of EdDSA.

(adam)