docs: update cross compilation section from autotools to meson

fixes #12934

Author: Mic92

doc/manual/source/development/building.md

@@ -195,29 +195,24 @@ Nix uses a string with the following format to identify the *system type* or *pl
 <cpu>-<os>[-<abi>]
 ```
 
-It is set when Nix is compiled for the given system, and based on the output of [`config.guess`](https://github.com/nixos/nix/blob/master/config/config.guess) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.guess)):
+It is set when Nix is compiled for the given system, and based on the output of meson's [host_machine information](https://mesonbuild.com/Reference-manual_builtin_host_machine.html)>
 
 ```
 <cpu>-<vendor>-<os>[<version>][-<abi>]
 ```
 
-When Nix is built such that `./configure` is passed any of the `--host`, `--build`, `--target` options, the value is based on the output of [`config.sub`](https://github.com/nixos/nix/blob/master/config/config.sub) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.sub)):
+When cross-compiling Nix with Meson for local development, you need to specify a [cross-file](https://mesonbuild.com/Cross-compilation.html) using the `--cross-file` option. Cross-files define the target architecture and toolchain. When cross-compiling Nix with Nix, Nixpkgs takes care of this for you.
+
+In the nix flake we also have some cross-compilation targets available:
 
 ```
-<cpu>-<vendor>[-<kernel>]-<os>
+nix build .#nix-everything-riscv64-unknown-linux-gnu
+nix build .#nix-everything-armv7l-unknown-linux-gnueabihf
+nix build .#nix-everything-armv7l-unknown-linux-gnueabihf
+nix build .#nix-everything-x86_64-unknown-freebsd
+nix build .#nix-everything-x86_64-w64-mingw32
 ```
 
-For historic reasons and backward-compatibility, some CPU and OS identifiers are translated from the GNU Autotools naming convention in [`configure.ac`](https://github.com/nixos/nix/blob/master/configure.ac) as follows:
-
-| `config.guess`             | Nix                 |
-|----------------------------|---------------------|
-| `amd64`                    | `x86_64`            |
-| `i*86`                     | `i686`              |
-| `arm6`                     | `arm6l`             |
-| `arm7`                     | `arm7l`             |
-| `linux-gnu*`               | `linux`             |
-| `linux-musl*`              | `linux`             |
-
 ## Compilation environments
 
 Nix can be compiled using multiple environments: