--freeze1 should be the default for hadrian

Summary

As a newcomer to Hadrian, I don't yet have a working understanding of all the things I need to do. Which means I'm often typing in hadrian commands by hand, and if I ever forget --freeze1 it goes and builds a bunch of stuff all over again, which usually borks my staged compiler. Fixing this often takes me roughly an hour of figuring out the last working version of source, and then waiting for a rebuild.

This is an absolutely awful experience. Rebuilding with the behavior marked by --freeze1 as a contributor to GHC is, in my experience, 100x more common than wanting to rebuild all the stages, and the default behavior should reflect that.

Steps to reproduce

Run ./hadrian/build-cabal after doing any amount of work

Expected behavior

Hadrian should not completely bork my environment because I forgot a flag.