exim: 4.92.3 -> 4.93.0.4
exim: 4.92.3 -> 4.93.0.4

As per the updating notes[1], DISABLE_TLS replaces SUPPORT_TLS.
The build system also wants you to choose between OpenSSL and GnuTLS.
Since we were using OpenSSL until now, I chose that.

[1]: https://git.exim.org/exim.git/blob_plain/885bb037cb791e057de2105bb3790c6135914c62:/src/README.UPDATING

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs