[Windows] Enable ARM64X build

[dongle-the-gadget]

Feature or enhancement

Proposal:

Currently, CPython offers separate x64 and ARM64 builds for Windows. This poses a challenge that users will need both installed in order for apps using x64 emulation and native ARM64 apps to use the Python interpreter.
This proposal suggests providing ARM64X (which is combined ARM64 native + ARM64EC) DLLs for CPython, allowing both native ARM64 apps and x64 emulated apps to use a single Python install.
Windows versions that do not provide native x64 emulation (Windows 10) will simply use the ARM64 binary within ARM64X, so there is no change to current behavior on those systems.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

[StanFromIreland]

CC @zooba

[zooba]

I'd be a bit concerned about the size increase - most of python3x.dll is code, so it'll probably nearly double in size, and I don't think everyone needs this.

Having a build configuration to enable the mode is the starting point anyway. Someone will need to do some experiments anyway before we commit to making it our standard release. But once the build option is there, anyone who needs it can do it, and anyone else who wants to release it can do it easily. I'll rename the request to reflect that.