CMakeLists.txt: use standard syntax for cp

[barracuda156]

Use standard cp syntax to avoid failures

[G-Ragghianti]

What failures does this avoid? cp -a is almost functionally equivalent to cp -pPR.

[barracuda156]

What failures does this avoid? cp -a is almost functionally equivalent to cp -pPR.

Yes, but it is not supported with some versions of cp. And then the build fails with invalid option.

[G-Ragghianti]

OK, so the change to to convert the GNU -a option to POSIX options. I wasn't sure how this would affect symlinks, but my tests look fine. Thanks.

[barracuda156]

From experience, it works as expected as a replacement for -a.

[G-Ragghianti]

The checks were not running due to an oversight in the self-hosted meta runner. I've fixed this, and the jobs are running now.

[barracuda156]

Thanks for merging!