TEST: Update example scripts for cmake feature

[jamesbeyond]

Summary of changes

This PR is the preparation for the Cmake branch test by

• adding a cmake dummy option
• overwrite mbed-os.lib instead of remove mbed-os.lib in CI

CI will need this option to enable the cmake branch test

Impact of changes

Migration actions required

Documentation

Not required

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Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

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[ciarmcom]

@jamesbeyond, thank you for your changes.
@ARMmbed/mbed-os-tools @ARMmbed/mbed-os-maintainers please review.

[jamesbeyond]

Hi @0xc0170 this PR is ready

[0xc0170]

CI started

[mbed-ci]

Jenkins CI Test : ✔️ SUCCESS

Build Number: 1 | 🔒 Jenkins CI Job | 🌐 Logs & Artifacts

CLICK for Detailed Summary

jobs	Status
jenkins-ci/mbed-os-ci_unittests	✔️
jenkins-ci/mbed-os-ci_build-ARM	✔️
jenkins-ci/mbed-os-ci_build-GCC_ARM	✔️
jenkins-ci/mbed-os-ci_greentea-test	✔️
jenkins-ci/mbed-os-ci_dynamic-memory-usage	✔️
jenkins-ci/mbed-os-ci_cloud-client-pytest	✔️