Fix runit install steps for gcc 14

What does this merge request do and why?

I just finished setting up GDK on my Linux refresh where I'm running Fedora. The steps to compile runit no longer work with Fedora 42 unless you modify the source before trying to compile it.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Run the script in a new Fedora 42 install, and ensure you have the C development group installed.

sudo dnf group install c-development

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This MR references an issue describing the change.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.