Auto-load buildenv when loading a compiler module (like GCC)

We can improve the user experience with EESSI by auto-loading a buildenv when a user loads a compiler module like GCC. That way they don't need to know anything about buildenv, the compiler "just works" and binaries are automatically rpath-ed.

We would need to create compiler-only buildenv modules (like buildenv-default-GCC-13.3.0.eb) but that would be very easy. We would also need to protect the loading of the buildenv module from the compiler module so that it is not done when we are inside an EasyBuild build session. This would mean having a hook that injects a protected load (via modluafooter).