Generate dummy-ghc from raw ghc source #2124

Job	Run time
cabal	26s
maintainer-scripts	8s
multi-target	24s
cabal-doExactConfig	29s
nix-build	1m 4s
runghc	24s
shellFor-hoogle	17s
shellFor-multiple-package	13s
shellFor-not-depends	25s
shellFor-single-package	16s
tests-benchmarks	10s
unit-tests	10s
build-extra-hackages	9s
docs	44s
hix	40s
hydra-ifdLevel-0-and-1	14s
hydra-ifdLevel-2	11s
hydra-ifdLevel-3-and-ghc-8-10	10s
plan-extra-hackages	10s
check-materialization-concurrency	23s
check-path-support	12s
closure-size	7s
haskell-nix-roots-do-not-require-IFDs	10s
hix-cabal	24s
hydra-ifdLevel-3-and-ghc-9-2	11s
hydra-ifdLevel-3-and-not-ghc-8-10-or-9-2	10s
nix-tools	39s
hydra-without-remote-builders	1m 43s
update-docs	8s
	10m 51s

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