libgcrypt: updated to 1.8.4

Noteworthy changes in version 1.8.4:
* Bug fixes:
  - Fix infinite loop due to applications using fork the wrong
    way.
  - Fix possible leak of a few bits of secret primes to pageable
    memory.
  - Fix possible hang in the RNG (1.8.3 only).
  - Several minor fixes.

* Performance:
  - On Linux always make use of getrandom if possible and then use
    its /dev/urandom behaviour.

(adam)