[C] Fix regression in cmake version in codespaces

[vaavva]

Purpose

• Codespaces no longer has a new enough version of cmake by default - this adds it to the setup steps. Fixes https://github.com/Azure-Samples/MqttApplicationSamples/issues/70
• Also fixes a segfault in the getting started sample

Checklist

• [x] I have read the contribution guidelines.
• I submitted this PR against the correct branch:
  • [x] This pull-request is submitted against the main branch.
  • [x] I have merged the latest main branch prior to submission and re-merged as needed after I took any feedback.
  • [x] I will squash my changes into one with a clear description of the change when I complete the PR.

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

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What to Check

Verify that the following are valid

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Other Information