"tool: command not found"

Dear maintainers,

I'm trying to test a ghc branch with linear types enabled. ghc-8.6.5 is on the path. I'm building hackage.head on Centos 7. I'm running:

sudo yum install -y pwgen
cabal update
cabal install hackage-repo-tool
PATH="$(pwd)/ci:/home/centos/.cabal/bin:$PATH" GHC=<path_to_ghc_with_linear_types> EXTRA_HC_OPTS=-dcore-lint ./run-ci

run-ci is failing with

Found GHC 8.9.0.20191023.
Marking singletons as broken due to #17405
Marking vinyl as broken due to #17405
++ pwd
+ cabal new-run head-hackage-ci -- test-patches --extra-cabal-fragment=/home/centos/head.hackage/ci/run/deps.cabal.project --patches=../../patches --with-compiler=/home/centos/ghc/install_dir/bin/ghc --expect-broken=singletons --expect-broken=vinyl --cabal-option=-j '--ghc-option="-dcore-lint"'
Up to date
Warning: The update command is a part of the legacy v1 style of cabal usage.

Please switch to using either the new project style and the new-update command
or the legacy v1-update alias as new-style projects will become the default in
the next version of cabal-install. Please file a bug if you cannot replicate a
working v1- use case with the new-style commands.

For more information, see: https://wiki.haskell.org/Cabal/NewBuild

Downloading the latest package list from hackage.haskell.org
To revert to previous state run:
    cabal update --index-state='2019-11-05T14:06:40Z'
Resolving dependencies...
No packages need to be fetched. All the requested packages are already local
or cached locally.
/home/centos/head.hackage/ci/build-repo.sh: line 173: tool: command not found
head-hackage-ci: Received ExitFailure 127 when running
Raw command: build-repo.sh build-repo

After some poking around I can't discover what provides the missing tool command. Any hints welcome.

I might also be using the wrong procedure to test ghc with the packages in hackage.head. I'll be thankful to be corrected about that as well.