[release/10.0] Add support for Visual Studio 2026 CMake generator for gen-buildsys.cmd

[iikuzmychov]

Backport of #120580 to release/10.0

Customer Impact

• Customer reported
• Found internally

The repo cmake msbuild generator is missing support for VS 2026 in release/10.0 branch. It makes it hard to work with the repo C/C++ code in VS 2026.

Regression

• Yes
• No

Testing

Verified that gen-buildsys.cmd selects the Visual Studio 18 2026 generator when %_VSVersion% is 18.0.

Risk

Low. No impact to skipping binaries.

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Adds support for the Visual Studio 18 2026 CMake generator in eng/native/gen-buildsys.cmd.

• Handles %_VSVersion% == "18.0" similarly to the existing Visual Studio 2022 case.
• Does not change behavior for other Visual Studio versions.

Testing:

• Verified that gen-buildsys.cmd selects the Visual Studio 18 2026 generator when %_VSVersion% is 18.0.

[Copilot]

Pull request overview

This PR adds support for the Visual Studio 2026 CMake generator in the native build system configuration script. The change enables the build system to recognize and use Visual Studio 18 (2026) when generating build files.

• Adds a conditional check for VS version 18.0 to set the CMake generator to "Visual Studio 18 2026"
• Follows the existing pattern established for VS 2022 (version 17.0)
• Placed appropriately before the VS 2022 check to handle newer versions first

[jkotas]

Thanks

[jkotas]

This was fixed in main by #120580 . I see you have submitted your change against release/10.0 branch. We require justification for all backport to release branches.

Could you share why you would like to see this change backported to release/10.0?

[iikuzmychov]

Ah, sorry, I haven't seen that this is already fixed in main brach. Basically why I created this PR is because I wanted to debug last stable version from release/10.0. I've tried to run .\build.cmd -vs CoreClr.sln or smth like this and got an error. During investigation I found that the issue is an absent condition within this .bat. I found no fixes for this within this branch so I decided to make a PR