This reduces dependencies. The speed of the code here is uimportant, because we
hash only a tiny amount of input data.
Debian and Ubuntu currently build without repart, see
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=976959
> repart requires openssl and so far I tried to avoid linking against
> both gnutls and openssl.
Co-authored-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>