Assuming you're just using git for conveniently applying local
downstream patches, you don't need the git repo to exist once
getting to the build stage. IOW just delete the .git dir after
applying patches before running a build.
...then what do you do if the build fails and you want to
edit/update the patch before retrying? "Blow away your .git
tree every time you build and reconstitute it somehow later"
doesn't seem like a very friendly thing to require...
+1. This option is disconnected with sustaining engineering reality
IMHO: tons of interactive rebases, adding and dropping patches,
re-orderings - so previous existing patches can allow the new ones (or
even existing ones) to become clean cherry-picks - in between patch sets
being worked on, bisections before continuing all this, etc.