Do not fail when the setup executable does not exist when checking for the windows clean hack.
Do not fail when the setup executable does not exist when checking
for the windows clean hack.

This would cause exceptions when using a cached setup executable,
making parallel builds on Windows completely unusable.

thomie/cabal,gridaphobe/cabal,triplepointfive/cabal,valderman/cabal,mydaum/cabal,enolan/cabal,garetxe/cabal,themoritz/cabal,kolmodin/cabal,sopvop/cabal,rimmington/cabal,ian-ross/cabal,fugyk/cabal,ian-ross/cabal,trskop/cabal,headprogrammingczar/cabal,thomie/cabal,mydaum/cabal,edsko/cabal,lukexi/cabal,christiaanb/cabal,corngood/cabal,mmakowski/cabal,mightybyte/cabal,ghc-android/cabal,valderman/cabal,themoritz/cabal,garetxe/cabal,headprogrammingczar/cabal,Peaker/cabal,enolan/cabal,trskop/cabal,x-y-z/cabal,thoughtpolice/cabal,martinvlk/cabal,mightybyte/cabal,randen/cabal,seereason/cabal,randen/cabal,plow-technologies/cabal,Helkafen/cabal,Heather/cabal,thoughtpolice/cabal,kolmodin/cabal,Helkafen/cabal,kosmikus/cabal,plumlife/cabal,martinvlk/cabal,Peaker/cabal,typelead/epm,gridaphobe/cabal,plumlife/cabal,edsko/cabal,sopvop/cabal,ghc-android/cabal,sopvop/cabal,gbaz/cabal,lukexi/cabal,beni55/cabal,bennofs/cabal,triplepointfive/cabal,rimmington/cabal,fugyk/cabal,x-y-z/cabal,typelead/epm,christiaanb/cabal,anton-dessiatov/cabal,corngood/cabal,kosmikus/cabal,plow-technologies/cabal,Heather/cabal,themoritz/cabal,gbaz/cabal,mmakowski/cabal,eric-stanley/cabal,beni55/cabal,anton-dessiatov/cabal,eric-stanley/cabal,bennofs/cabal,seereason/cabal