Build std variant on windows

[AntoinePrv]

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

[AntoinePrv]

I tried adding in rust-std-x86_64-pc-windows-gnu #280 but it cannot be installed on windows due to __unix constraint.

Error:   × failed to solve requirements of environment 'dev' for platform 'win-64'
  ├─▶   × failed to solve the environment
  │
  ╰─▶ Cannot solve the request because of: rust-std-x86_64-pc-windows-gnu * cannot be installed because
      there are no viable options:
      └─ rust-std-x86_64-pc-windows-gnu 1.94.0 would require
         └─ __unix *, for which no candidates were found.

@baszalmstra @isuruf I tried following conversation from #227 #170 but still not sure if this is the best approach.
Somehow it works for the other to windows std package but not this one.
Is this the correct fix?

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found it was in an excellent condition.

I do have some suggestions for making it better though...

For recipe/meta.yaml:

• ℹ️ Use of posix package on windows is deprecated. Use m2-base.
• ℹ️ The recipe is not parsable by parser conda-souschef (grayskull). This parser is not currently used by conda-forge, but may be in the future. We are collecting information to see which recipes are compatible with grayskull.
• ℹ️ The recipe is not parsable by parser conda-recipe-manager. The recipe can only be automatically migrated to the new v1 format if it is parseable by conda-recipe-manager.

_{This message was generated by GitHub Actions workflow run https://github.com/conda-forge/conda-forge-webservices/actions/runs/25003424018. Examine the logs at this URL for more detail.}

[isuruf]

Somehow it works for the other to windows std package but not this one.

for windows-msvc, it's built as part of building the compiler, so you don't need to build it again in windows.

[conda-forge-admin]

Hi! This is the friendly conda-forge automerge bot!

I considered the following status checks when analyzing this PR:

• linter: passed
• azure: passed
• github-actions: passed

Thus the PR was passing and merged! Have a great day!