labs/lab-04: Check x86_64 version.

[teodutu]

#124 Introduced x86_64 labs. Each of them needs to be checked for the following:

1. Make sure all guides work
2. Go through the reading section and fix all inconsistencies, typos, and add whatever information you think is missing.
3. For each task:
   a. Make sure it compiles and runs (both support and solution)
   b. Make sure the checker verifies the correct thing
   c. Make sure the solution correctly implements the task

This issue is done when the items above are completed for lab-04. Fix any mistakes you find, then raise a PR following these steps [1] and request review from me (@teodutu). Make sure you follow the steps at [1], especially about formatting the commit. Watch for linter failures after creating the PR and fix them.

Add Fix #136 in the commit message or PR description to automatically close this issue once the PR is merged.
In the unlikely event that there's nothing broken in the lab, just leave a comment that says so and close this issue.

[1] https://github.com/cs-pub-ro/hardware-software-interface/blob/main/CONTRIBUTING.md#pull-requests