libxcrypt

[atalii]

libcrypt (generally from glibc) doesn't support yescrypt, which is used by default in Debian and Arch (among others). Accordingly, password hashing is broken on all of those. We need to use libxcrypt instead.

• Cleanly return when crypt fails. Kind of unacceptable that it just fails to a stack trace.
• Make sure to link against libxcrypt.