Update Windows build instructions for CMake 4.0+ support, Spectre-mitigated libraries, and VS 2026

[Copilot]

Users building on Windows with VS2019, VS2022, or VS2026 need updated documentation for proper build environment setup.

Changes

CMake version requirements:

• Documented that CMake 4.0+ is now supported
• Specified minimum versions: CMake 3.14+ for VS2019, CMake 3.21+ for VS2022, CMake 4.2+ for VS2026

Visual Studio installation section:

• Generalized installation instructions to cover VS 2019, 2022, and 2026
• Added introductory text explaining similarities across versions
• Documented MSVC toolset version mapping (v142 for VS 2019, v143 for VS 2022, v145 for VS 2026)
• Changed section headers to "(Example)" format to indicate reference examples
• Added comprehensive VS2022 installation instructions with Spectre-mitigated libraries:
  • MSVC v143 - VS 2022 C++ x64/x86 Spectre-mitigated libs (Latest)
  • ARM/ARM64 variants for cross-compilation
• Updated Spectre-mitigated libraries note to be version-agnostic, covering all VS versions
• Documented location in VS Installer: Individual components → Compilers, build tools, and runtimes

Documentation structure improvements:

• Reorganized VS installation sections with clear hierarchy showing examples for VS 2022 and VS 2019
• Updated all build instruction references to include VS 2019, 2022, and 2026
• Enhanced Known Issues section with CMake version compatibility information for all three VS versions

File: docs/building/windows-instructions.md

• Fixes Build instructions: CMake < 4.0 and spectre-mitigation #7467

Original prompt

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This section details on the original issue you should resolve

<issue_title>Build instructions: CMake < 4.0 and spectre-mitigation</issue_title>
<issue_description>System Information (please complete the following information):

• OS & Version: Windows 11, VS2022
• ML.NET Version: main from github 17th May 2025

Describe the bug
To compile the project on Windows:
CMake 4.0.2 return error "path not found"
Spectre-mitigated libraries are needed in VS2022

To Reproduce
Steps to reproduce the behavior:

1. Clean machine
2. Install VS2022 and follow instructions on developer page
3. Install latest CMake
4. Observe errors trying to build Native libraries

Additional context
Minor update needed https://github.com/dotnet/machinelearning/blob/main/docs/building/windows-instructions.md on Individual Components needed and probably a notice on using CMake <4.0.0
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Build instructions: CMake < 4.0 and spectre-mitigation #7467

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[ericstj]

Actually CMake 4.0 should work just fine. I needed this for 694bc60.

VS 2026 also works now.

@copilot can you please update the docs accordingly?

[Copilot]

Actually CMake 4.0 should work just fine. I needed this for 694bc60.

VS 2026 also works now.
...

Updated the documentation to reflect CMake 4.0+ support. Removed the incompatibility warnings and added a note that CMake 4.0 and later versions are now supported. Commit: 94d6cdf

[ericstj]

@copilot address feedback