Avoid spurious rebuilds on feature branches

[Jason Conroy]

In keeping with the standard dev workflow from the manual, I am 
frequently testing changes with `make -j 8 && ./pre-inst-env guix 
<command>`. But if I switch my workspace from one branch to 
another, git seems to touch files in a way that causes `make` to 
do a full rebuild, even when the new branch is very similar to the 
old one.

The rebuild isn't really a problem, except that I lose 20 minutes 
of productivity. Are there any workflow hacks that might improve 
this situation?

Regards,

Jason