Use the file() CREATE_LINK command to create symlinks when running ake

[jim-p-w]

This PR replaces the cmake execute_process() command with the file() command to create symlinks.

Using execute_process to make symlinks is expensive; it spawns a new cmake process.
The file() command is more efficient; it makes the symlink in the currently executing cmake process.

This was tested by running cmake directly against a clone of the MPAS-Model repository, as well
as running cmake against a clone of the mpas-bundle repository (which include MPAS-Model).

[mgduda]

@svahl991 -- @jim-p-w suggested adding you as a reviewer as well. If you'd like, I can first add you as a collaborator, then add you as a formal reviewer. Otherwise, if you'd just like to comment on the PR, that should be fine, too.

[svahl991]

@svahl991 -- @jim-p-w suggested adding you as a reviewer as well. If you'd like, I can first add you as a collaborator, then add you as a formal reviewer. Otherwise, if you'd just like to comment on the PR, that should be fine, too.

This looks fine to me, but I will also pass this buck down the line to @fmahebert, who was the one who put together all the PR's similar to this one in the JEDI repositories.

[fmahebert]

This matches what I'd expect based on what I did in JEDI.

My only suggestion would be to make sure cmake_minimum_required(VERSION 3.14) is specified, for CREATE_LINK support.

Thanks, @jim-p-w !

(Context for those not following JEDI repo developments: doing this change across most of jedi-bundle repos eliminated ~4000 subprocess launches. That saves ~7 seconds of CMake configuration time on a Apple M2 based dev system, and >60 seconds on one HPC system with a network filesystem (and perhaps policies that limit process launching?). The benefit in any particular repo would be proportional to the number of symlinks/processes involved in the configuration.)

[jim-p-w]

@fmahebert Thanks for the suggestion. I changed cmake_minimum_required from 3.12 to 3.26 (which was released in 2023 and is the oldest version currently available on derecho).

[fmahebert]

@jim-p-w sounds good, thanks — for those of at JCSDA, we've had access to CMake 3.27+ since spack-stack 1.8 from two years ago, so shouldn't be a problem.

[fmahebert]

non-expert review