Update multithreading-and-locales.md

[Antonz0]

Wrong setlocale() reference, it should be a C runtime function, not a preprocessor macro.

[ghost]

All CLA requirements met.

[PRMerger10]

@Antonz0 : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[opbld32]

Docs Build status updates of commit 13d99b1:

✅ Validation status: passed

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docs/parallel/multithreading-and-locales.md	✅Succeeded

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[Jak-MS]

@TylerMSFT

Can you review this PR?

IMPORTANT: When this content is ready to merge, you must add #sign-off in a comment or the approval may get overlooked.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[colin-home]

At least we were consistent. This change looks good to me. Thanks, @Antonz0

[colin-home]

#sign-off

[PRMerger18]

Invalid command: '#sign-off'. Only the assigned author of one or more file in this PR can sign off. @TylerMSFT

[opbld31]

Docs Build status updates of commit 13d99b1:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/parallel/multithreading-and-locales.md	✅Succeeded

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the docs.microsoft.com contributor guides
• Post your question in the Docs support channel