Use a CMake function provided by CIME

[billsacks]

Description of changes

Use a new CMake function provided by CIME in place of some messy CMake code.

Requires cime6.1.137

Specific notes

Contributors other than yourself, if any: none

CTSM Issues Fixed (include github issue #): none

Are answers expected to change (and if so in what way)? no

Any User Interface Changes (namelist or namelist defaults changes)? no

Does this create a need to change or add documentation? Did you do so? no

Testing performed, if any:

• Ran unit tests on my Mac

[ekluzek]

Again thanks so much @billsacks ! This is a great code health improvement. I ask a question about the need to still remove shr_mpi_mod.F90 in light of cime6.1.137. But, otherwise this is good to come in.

Like your other PR, we'll need to wait for Derecho to come back up. I'll test it on Derecho just to show it works for me and then merge it in. Then I'll do the other PR, and do more tests with it (that'll also include this as well).

[billsacks]

I'll test it on Derecho just to show it works for me and then merge it in.

It seems like you saw this, but I just wanted to call out: Note that this requires cime6.1.137 or later. That's the main reason I kept this separate from #3581 -- #3581 can come in any time, but this one will need to be coordinated with a cime update.

[ekluzek]

This is blocked by #3583 for the submodule update part of this.