allow --compiler and --mpilib

[jedwards4b]

This PR allows ctest to use the new --compiler and --mpilib options in scripts_regression_tests.py
by using env variables CIME_COMPILER and CIME_MPILIB

Test suite: CIME_COMPILER=nag ./cime.ctest.hobart
Test baseline:
Test namelist changes:
Test status: bit for bit
Fixes #1770
Fixes #1281

User interface changes?:

Update gh-pages html (Y/N)?:

Code review:

[billsacks]

Thanks a lot for doing this, and for adding cron jobs with some alternative compilers!

My one comment relates to how CIME_COMPILER and CIME_MPILIB are passed in to cmake. I find it confusing when things are passed in via environment variables, and this can cause hard-to-track-down problems when someone happens to have something set in their environment for some other reason.

I feel like the better way to pass things in to cmake is to use something like:

cmake -D CIME_COMPILER=something

Would it be feasible to use that approach here? If there is some large difficulty in doing this, I can live with the current implementation, but I'd prefer to avoid environment variables if possible.

[jedwards4b]

I gave them CIME_ prefix because that way it's unlikely to conflict with anything else. I don't think that this is worth the effort it would take to change, but you are welcome if you want to.

[billsacks]

I gave them CIME_ prefix because that way it's unlikely to conflict with anything else. I don't think that this is worth the effort it would take to change, but you are welcome if you want to.

Okay, I can live with this, but can you please add documentation at the top of the two cmake files documenting the usage and the possible environment variables that can affect operation of these scripts? Once you have done that, I'll accept this PR.

[jedwards4b]

added comments