Hadrian build fails on Windows

As of 509d5be6,

$ hadrian/build.cabal.sh -j5 --flavour=Quick
...
$ hadrian/build.cabal.sh -j5 --flavour=Quick
| ContextData oracle: resolving data for 'iserv' (Stage1, v)... 
| Configure package 'iserv' 
Configuring iserv-8.7.1... 
creating
C:\msys64\home\ben\ghc\builds\0\project-0\_build\stage1\utils\iserv\build
"C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe" "--numeric-version"
]0;1s (99%)C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe is version 
8.7.20181126 
"C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc-pkg.exe" "--version"
C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc-pkg.exe is 
version 8.7.20181126 
"C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe" "--supported-languages"
"C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe" "--info" 
Reading installed packages... 
"C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc-pkg.exe" "dump" "--global" "-v0" "--global-package-db=C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage1/lib/package.conf.d" 
"C:/msys64/home/ben/ghc/builds/0/project-0/_build/stage0/bin/ghc.exe" "--print-libdir" "-ghcversion-file=C:/msys64/home/ben/ghc/builds/0/project-0/_build/generated/ghcversion.h" 
CallStack (from HasCallStack): 
  die', called at .\Distribution\Simple\Configure.hs:969:20 in Cabal-2.5.0.0-inplace:Distribution.Simple.Configure 
  configureFinalizedPackage, called at .\Distribution\Simple\Configure.hs:467:12 in Cabal-2.5.0.0-inplace:Distribution.Simple.Configure
  configure, called at .\Distribution\Simple.hs:596:20 in Cabal-2.5.0.0-inplace:Distribution.Simple
  confHook, called at .\Distribution\Simple\UserHooks.hs:67:5 in Cabal-2.5.0.0-inplace:Distribution.Simple.UserHooks
  configureAction, called at .\Distribution\Simple.hs:178:19 in Cabal-2.5.0.0-inplace:Distribution.Simple
  defaultMainHelper, called at .\Distribution\Simple.hs:148:3 in Cabal-2.5.0.0-inplace:Distribution.Simple
  defaultMainWithHooksNoReadArgs, called at src\Hadrian\Haskell\Cabal\Parse.hs:145:14 in main:Hadrian.Haskell.Cabal.Parse
hadrian.exe: Encountered missing dependencies:
libiserv ==8.7.*
]0;FinishedshakeArgsWith   0.003s    0%
Function shake  0.442s    2%
Database read   0.851s    3%  =
With database   0.033s    0%
Running rules  20.749s   93%  =========================
Total          22.079s  100%
Error when running Shake build system:
  at src/Main.hs:58:30-42:
* Depends on: test
  at src/Rules/Test.hs:109:5-9:
* Depends on: _build/stage1/lib/bin/ghc-iserv.exe
  at src/Development/Shake/Internal/Rules/Oracle.hs:157:43-68:
* Depends on: OracleQ (ContextDataKey (Context {stage = Stage1, package = Package {pkgType = Program, pkgName = "iserv", pkgPath = "utils/iserv"}, way = v}))
  at src/Hadrian/Haskell/Cabal/Parse.hs:202:5-36:
* Depends on: _build/stage1/utils/iserv/setup-config
* Raised the exception:
ExitFailure 1

(Ignore garbage characters due to Window's broken ANSI console support).

This seems to only be reproducible on Windows.