How to cross compile for ARM with MSVC?

Nobody has claimed this yet.

Normally when compiling with MSVC, you select the cross compilation target ("host" in the cross file) by running a script that sets up the environment (`PATH`, `LIB`) according to the desired host environment; the `cl.exe` in path is then the one for the chosen architecture, and `LIB` points to the directories containing libraries for this architecture.

If trying to run meson in such an environment, the default native compiler is also detected as `cl` from the path, a dialog box saying "The image file c:\...\sanitycheckc.exe is valid, but is for a machine type other than the current machine" appears, and meson fails with the following error message:

```
meson.build:25:0: ERROR: Could not invoke sanity test executable: [WinError 216] This version of %1 is not compatible with the version of Windows you're running. Check your computer's system information and then contact the software publisher.
```

How is one supposed to set up cross compilation with Meson with the MSVC compiler, when you can only have one compiler in `PATH` and one `LIB` set of directories in the environment at a time?

Start with the cross-file setup and the sanity-check invocation reported at meson.build:25. Review how Meson handles the MSVC environment and target executable, then document a supported ARM cross-compilation workflow or clarify the limitation; the issue is done when the setup and expected behavior are clear.

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