Hadrian fails to invoke testsuite runner on Windows

The Windows hadrian job fails with,

# ghc-config (for _build/test/ghcconfig)
ghc-config.exe: C:/GitLabRunner/builds/e963ee11/0/ghc/ghc/_build/install/bin/ghc: readCreateProcess: invalid argument (Exec format error)
Error when running Shake build system:
  at want, called at src\Main.hs:89:30 in main:Main
* Depends on: test
  at need, called at src\Rules\Test.hs:85:9 in main:Rules.Test
* Depends on: _build/test/ghcconfig
* Raised the exception:
user error (Development.Shake.cmd, system command failed
Command line: _build/test/bin/ghc-config.exe C:/GitLabRunner/builds/e963ee11/0/ghc/ghc/_build/install/bin/ghc
Exit code: 1
Stderr:
ghc-config.exe: C:/GitLabRunner/builds/e963ee11/0/ghc/ghc/_build/install/bin/ghc: readCreateProcess: invalid argument (Exec format error)
)

I suspect the issue here is that we are trying to use CreateProcess to run a shell script.