Add cmake/ to release tarballs via concatenation

The solution using append was reported not to work, but additionally it
would use the contents of the checked-out source tree instead of the git
tag or commit. This uses `git archive`, so it will use the right commit,
and at least for me (with GNU tar) it seems to work as intended.

Should fix #53281.

Reviewed By: kwk

Differential Revision: https://reviews.llvm.org/D121972