Make building optional when installing in install-dist.p6
Make building optional when installing in install-dist.p6

When --build-only is used in a previous step, we may skip it at
installation time.

softmoth/rakudo,MasterDuke17/rakudo,salortiz/rakudo,tony-o/rakudo,labster/rakudo,tony-o/rakudo,softmoth/rakudo,labster/rakudo,rakudo/rakudo,tbrowder/rakudo,tbrowder/rakudo,rakudo/rakudo,rakudo/rakudo,softmoth/rakudo,salortiz/rakudo,tony-o/rakudo,salortiz/rakudo,rakudo/rakudo,salortiz/rakudo,nbrown/rakudo,rakudo/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,tony-o/rakudo,softmoth/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,labster/rakudo,nbrown/rakudo,nbrown/rakudo,softmoth/rakudo,MasterDuke17/rakudo,tony-o/rakudo,salortiz/rakudo,nbrown/rakudo,rakudo/rakudo,labster/rakudo,labster/rakudo,salortiz/rakudo,nbrown/rakudo,nbrown/rakudo,labster/rakudo,tbrowder/rakudo,tony-o/rakudo,tbrowder/rakudo,tbrowder/rakudo