Adding FATES subdirectories to PF unit build fails

We will want to bring in FATES subdirectories to the main PF unittesting so that we can test both things outside of and inside FATES. And it could be good to run all of the CTSM and FATES tests all together.

But adding FATES subdirectories to the PF unit-test build fails with errors in the FATES endrun calls.

Adding FATES subdirectories to the PF unit build gets a bunch of errors on endrun calls in FATES code like the following:

```
/glade/work/erik/ctsm_worktrees/newbranch/src/fates/radiation/TwoStreamMLPEMod.F90(1748): error #6498: The use-name for this local-name is not defined. [ERRMSG]
call endrun(msg=errMsg(sourcefile, 1748))
```

It works, if the build is run twice, but if you delete the unit test build directory, and run from scratch it doesn't work. So I'll remove this part.

_Originally posted by @ekluzek in https://github.com/ESCOMP/CTSM/pull/3699#discussion_r2714897531_