Create warning directive page

[Rageking8]

Fixes #4703

[prmerger-automator]

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[learn-build-service-prod]

Learn Build status updates of commit d06be5a:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/preprocessor/hash-error-directive-c-cpp.md	✅Succeeded
docs/preprocessor/hash-warning-directive-c-cpp.md	✅Succeeded

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[learn-build-service-prod]

Learn Build status updates of commit 6f18afe:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/preprocessor/hash-error-directive-c-cpp.md	✅Succeeded
docs/preprocessor/hash-warning-directive-c-cpp.md	✅Succeeded
docs/preprocessor/preprocessor-directives.md	✅Succeeded

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PRMerger Results

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Added File(s)	This PR contains added files. New files require human review.
File Change Percent	This PR contains file(s) with more than 30% file change.

[learn-build-service-prod]

Learn Build status updates of commit c523295:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/preprocessor/hash-error-directive-c-cpp.md	✅Succeeded
docs/preprocessor/hash-warning-directive-c-cpp.md	✅Succeeded
docs/preprocessor/preprocessor-directives.md	✅Succeeded
docs/preprocessor/toc.yml	✅Succeeded

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PRMerger Results

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Added File(s)	This PR contains added files. New files require human review.
Yaml File(s)	This PR includes changes to .yml file(s) owned by another author.
File Change Percent	This PR contains file(s) with more than 30% file change.

[Court72]

@TylerMSFT

Can you review the proposed changes?

When the changes are ready for publication, add a #sign-off comment to signal that the PR is ready for the review team to merge.

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

[TylerMSFT]

Thank you. I'll hang onto this but won't send it through now because we don't support this directive yet.