Log Message:
Update botan2 to version 2.19.4

Pkgsrc changes:
Add pkg-config override.

Changes From changelog:

* Fix a potential denial of service caused by accepting arbitrary
  length primes as potential elliptic curve parameters in ASN.1
  encodings. With very large inputs the primality verification
  can become computationally expensive. Now any prime field larger
  than 1024 bits is rejected immediately. Reported by Bing Shi.
  (GH #3914)

* Switch to using a constant time binary algorithm for computing
  GCD (GH #3912)

* Fix a bug in SHAKE_Cipher which could cause incorrect output
  if set_key was called multiple times. (GH #3192)

* Fix a bug in RSA-KEM encryption where the shared secret key
  was incorrectly not padded to exactly the byte length of the
  modulus. This would cause an incorrect shared key with ~1/256
  probability. (GH #3380)

* In RSA decryption and signature verification, reject bytestrings
  which are longer than the public modulus. Previously, otherwise
  valid signatures/ciphertexts with additional leading zero bytes
  would also be accepted. (GH #3380)

* Add support for short nonces in XTS (GH #3384 #3336)

* Fix NIST keywrap which was incorrect when wrapping 64-bit keys
  (GH #3384 #3340)

* Fix nonce handling bug in EAX (GH #3382 #3335)

* Fix a bug in PKCS11 AttributeContainer where adding an attribute
  that already existed could cause incorrect references to the
  existing attributes. (GH #3185)

* Apply patches which allow GCC 4.7 to compile Botan 2.x. Previously
  at least GCC 4.8 had been required. (GH #3273)

* Fix a build time problem affecting VCpkg (GH #3071)

* Fix a build problem affecting Windows ARM with Visual C++ (GH #3871)