* modules/rosenthal/packages/admin.scm (dinit): Update to 0.20.0.
[build-system]: Switch to gnu-build-system.
[arguments] <#:configure-flags>: Adjust accordingly.
<#:make-flags>: Set CXX and CXX_FOR_BUILD.
* modules/rosenthal/packages/admin.scm (tuigreet): New variable.
* modules/rosenthal/packages/rust-crates.scm (lookup-cargo-inputs)[tuigreet]:
New entry.