Relocatable builds
Relocatable builds

Use DESTDIR parameter and `cabal copy` so we can move our builds.

Useful for packaging purposes.

Some work required to remove the bits where building will mutate
the user's package DB, e.g. in the `PLATCABAL` target.

GaloisInc/HaLVM,thumphries/HaLVM,elijah513/HaLVM,mwotton/HaLVM,thumphries/HaLVM,rowhit/HaLVM,mwotton/HaLVM,rowhit/HaLVM,GaloisInc/HaLVM,elijah513/HaLVM,ggkitsas/HaLVM,ggkitsas/HaLVM,ggkitsas/HaLVM,mwotton/HaLVM,elijah513/HaLVM,GaloisInc/HaLVM,rowhit/HaLVM