Update pack.md

[mcfi]

Clarify the default pack value for ARM64EC

[PRMerger15]

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

[opbld31]

Docs Build status updates of commit ec65eb2:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/preprocessor/pack.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.

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[Jak-MS]

IMPORTANT: When this content is ready to merge, the reviewer 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]

@mcfi Thanks for the update. It should be visible online tomorrow.

[opbld30]

Docs Build status updates of commit ec65eb2:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/preprocessor/pack.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