[gha] ensure the FreeBSD build job fails when there are compilation failures

[andrurogerz]

Purpose

The FreeBSD build was silently failing for a week or so but the GitHub build job was succeeding anyway. This looks like a quirk in the vmactions/freebsd-vm action, where it reports the exit code of the last command run. This PR ensures the last command run is actually the cmake --build command.

Overview

• Move the tar command for the build output out of the VM and back to the job runner to ensure the last command run in the VM is cmake --build.
• Fix the build error introduced by 0cf4f74 by renaming FreeBSD's Platform::GetOSKernelPath with Platform::GetOSKernelVersion as was done for Linux.
• Update FreeBSD's Platform::GetOSBuild to report uname's release string rather than version, as was previously done for Linux.

Validation

Confirmed the FreeBSD build breaks in its current state by applying 0cf4f74 only.