ebcadbb2

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Unify --out-dir as the driver's single output sink

Rename the 'run' subcommand's --mutation-report-dir flag to --out-dir
to match the convention already established in assert-score.  Rename
the corresponding field on MutationDriverSettings to
mutationDriverSettingOutDir.

Move the report.txt write from Driver.runDriver into Mutate.runMutationMode,
right after writeMutationRunReport.  This way report.txt is always
written when --out-dir is set, even when --fail-fast triggers an
exitWith before control would otherwise return to runDriver.

mutationCheck.nix's buildPhase now passes --out-dir="$out" and the
installPhase is just the pre/postInstall hooks (no copy, no mkdir,
no tee).  Build failures (e.g. failed assertion under --fail-fast)
still abort before installPhase as they did before.