skip libatomic if mac (backport #565)

[mergify]

Description

skip libatomic if mac

This check is not correctly stopping -latomic from being used on all apple computers. This causes all downstream libraries to fail to link.

Fixes # (issue)
RoboStack/ros-jazzy#217

Is this user-facing behavior change?

Building

Did you use Generative AI?

No

Additional Information

---

This is an automatic backport of pull request #565 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 45756eb has failed:

On branch mergify/bp/jazzy/pr-565
Your branch is up to date with 'origin/jazzy'.

You are currently cherry-picking commit 45756eb.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CMakeLists.txt

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[fujitatomoya]

same here, just pick the original different to put here to resolve conflict.

[ahcorde]

Pulls: #568
Gist: https://gist.githubusercontent.com/ahcorde/b8d1597804afbce012ae8fce9deea582/raw/3baefef1a8ddad61a3426d0671fa4d8f084313ec/ros2.repos
BUILD args: --packages-above-and-dependencies rcutils
TEST args: --packages-above rcutils
ROS Distro: jazzy
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/19361

• Linux
• Linux-aarch64
• Linux-rhel
• Windows