bcrypt libc linux

brcypt is not available in libc's crypt() method on Debian 9. I would like to have used it for dovecot passwort storage.

Reasons:

• Debian does not want to differ from upstream glibc (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=149452)
• glibc does not want to include it because it is not on the list of NIST-recommended algorithms
  • https://sourceware.org/bugzilla/show_bug.cgi?id=2100
  • https://akkadia.org/drepper/sha-crypt.html

We shall use SHA-512 instead.