support compiler pin migrations for runtime constraints?

[beckermr]

We have several feedstocks that depend on the compiler version pins at runtime. When we bump the compiler versions globally without a migration, these runtime constraints cause broken environments and need manual maintenance. The feedstocks I know of that have this issue are

• compilers
• rubinenv
• mpich
• openmpi?
• camb?

It'd be nice to provide a migration via the bot for these runtime pins to help automate rebuilds.

Note that we do not need this migration for build environments and how we normally use these pins in conda-forge. This would be us supporting a bit more the usage of our compiler stack outside of conda-forge. Also implementing this will require some work in the bot which only looks at host for ABI stuff. I am personally happy to do that work, but I wanted to check that we think this is an ok thing for us to support.

Thoughts @conda-forge/core?

[jaimergp]

I've seen comments about this in the past (some devs who set up build envs for their workflow with conda), and while I am not super familiar with the migration stack, I am happy to learn more and help out here. You have my +1!