doc/stdenv/cross-compilation: Add 'Using `-static` outside a `isStatic` platform' (#344985)

`[Errno 8] Exec format error: './gdk3-scan'`

#### Using `-static` outside a `isStatic` platform. {#cross-static-on-non-static-platform}

Add `stdenv.cc.libc.static` (static output of glibc) to `buildInputs` conditionally on if `hostPlatform` uses `glibc`.

e.g.

```nix

{

  buildInputs = lib.optionals (stdenv.hostPlatform.libc == "glibc") [ stdenv.cc.libc.static ];

}

```

Examples of errors which this fixes.

`cannot find -lm: No such file or directory`

`cannot find -lc: No such file or directory`

::: {.note}

At the time of writing it is assumed the issue only happens on `glibc` because it splits the static libraries in to a different output.

::: {.note}

You may want to look in to using `stdenvAdapters.makeStatic` or `pkgsStatic` or a `isStatic = true` platform.

## Cross-building packages {#sec-cross-usage}

Nixpkgs can be instantiated with `localSystem` alone, in which case there is no cross-compiling and everything is built by and for that system, or also with `crossSystem`, in which case packages run on the latter, but all building happens on the former. Both parameters take the same schema as the 3 (build, host, and target) platforms defined in the previous section. As mentioned above, `lib.systems.examples` has some platforms which are used as arguments for these parameters in practice. You can use them programmatically, or on the command line: