Clarify that _O_TEXT is ANSI.

[davidmatson]

This constant was originally added before such a distinction was made; make it clear that _O_TEXT means ANSI text.

[prmerger-automator]

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

[learn-build-service-prod]

Learn Build status updates of commit c3b959c:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/c-runtime-library/reference/open-osfhandle.md	✅Succeeded
docs/c-runtime-library/reference/open-wopen.md	✅Succeeded
docs/c-runtime-library/reference/pipe.md	✅Succeeded
docs/c-runtime-library/reference/setmode.md	✅Succeeded
docs/c-runtime-library/reference/sopen-s-wsopen-s.md	✅Succeeded
docs/c-runtime-library/reference/sopen-wsopen.md	✅Succeeded
docs/c-runtime-library/text-and-binary-mode-file-i-o.md	✅Succeeded
docs/c-runtime-library/translation-mode-constants.md	✅Succeeded

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[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

[gewarren]

#sign-off

[prmerger-automator]

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

[davidmatson]

@Court72 - TylerMSFT is OOF, so someone else on his team approved. Can you enable that signoff for this PR? Thanks!