Improve VERSION/GIT_COMMIT_ID handling for sdist
Improve VERSION/GIT_COMMIT_ID handling for sdist

This makes `VERSION` updating a bit more robust (the file gets only
updated if its content would actually change), as well as moving the
dependency of `VERSION` and `GIT_COMMIT_ID` to the `sdist-ghc-prep`
target, as that's where it's actually needed.

This fixes the specialised target `make sdist-ghc` not properly
creating/updating the `VERSION` and `GIT_COMMIT_ID` files before
creating the ghc source-dist tarball, as well as avoiding stale
`VERSION` files.

sdiehl/ghc,vTurbine/ghc,TomMD/ghc,nkaretnikov/ghc,elieux/ghc,sgillespie/ghc,AlexanderPankiv/ghc,TomMD/ghc,ml9951/ghc,da-x/ghc,TomMD/ghc,sdiehl/ghc,wxwxwwxxx/ghc,green-haskell/ghc,GaloisInc/halvm-ghc,acowley/ghc,forked-upstream-packages-for-ghcjs/ghc,nathyong/microghc-ghc,acowley/ghc,sgillespie/ghc,ghc-android/ghc,christiaanb/ghc,anton-dessiatov/ghc,bitemyapp/ghc,GaloisInc/halvm-ghc,ezyang/ghc,wxwxwwxxx/ghc,vTurbine/ghc,nathyong/microghc-ghc,AlexanderPankiv/ghc,forked-upstream-packages-for-ghcjs/ghc,nathyong/microghc-ghc,sdiehl/ghc,nushio3/ghc,forked-upstream-packages-for-ghcjs/ghc,bitemyapp/ghc,fmthoma/ghc,fmthoma/ghc,sgillespie/ghc,ezyang/ghc,sdiehl/ghc,da-x/ghc,olsner/ghc,gcampax/ghc,ghc-android/ghc,mettekou/ghc,urbanslug/ghc,green-haskell/ghc,vikraman/ghc,olsner/ghc,ml9951/ghc,acowley/ghc,gcampax/ghc,mcschroeder/ghc,AlexanderPankiv/ghc,sgillespie/ghc,acowley/ghc,ghc-android/ghc,mettekou/ghc,anton-dessiatov/ghc,nkaretnikov/ghc,christiaanb/ghc,nathyong/microghc-ghc,mettekou/ghc,siddhanathan/ghc,ezyang/ghc,fmthoma/ghc,christiaanb/ghc,oldmanmike/ghc,TomMD/ghc,GaloisInc/halvm-ghc,oldmanmike/ghc,mcschroeder/ghc,anton-dessiatov/ghc,urbanslug/ghc,mcschroeder/ghc,snoyberg/ghc,mettekou/ghc,forked-upstream-packages-for-ghcjs/ghc,fmthoma/ghc,gcampax/ghc,gcampax/ghc,ml9951/ghc,oldmanmike/ghc,oldmanmike/ghc,tjakway/ghcjvm,AlexanderPankiv/ghc,urbanslug/ghc,shlevy/ghc,vTurbine/ghc,nushio3/ghc,gridaphobe/ghc,sdiehl/ghc,mettekou/ghc,acowley/ghc,ghc-android/ghc,mfine/ghc,vTurbine/ghc,ml9951/ghc,gridaphobe/ghc,oldmanmike/ghc,gcampax/ghc,da-x/ghc,forked-upstream-packages-for-ghcjs/ghc,GaloisInc/halvm-ghc,urbanslug/ghc,shlevy/ghc,mfine/ghc,bitemyapp/ghc,tjakway/ghcjvm,wxwxwwxxx/ghc,nushio3/ghc,vTurbine/ghc,mcschroeder/ghc,snoyberg/ghc,oldmanmike/ghc,nkaretnikov/ghc,urbanslug/ghc,acowley/ghc,AlexanderPankiv/ghc,siddhanathan/ghc,gridaphobe/ghc,mfine/ghc,nushio3/ghc,siddhanathan/ghc,ghc-android/ghc,christiaanb/ghc,wxwxwwxxx/ghc,tjakway/ghcjvm,elieux/ghc,ghc-android/ghc,tjakway/ghcjvm,shlevy/ghc,snoyberg/ghc,gridaphobe/ghc,elieux/ghc,mettekou/ghc,mcschroeder/ghc,olsner/ghc,shlevy/ghc,da-x/ghc,ml9951/ghc,vikraman/ghc,mfine/ghc,snoyberg/ghc,ezyang/ghc,anton-dessiatov/ghc,sdiehl/ghc,wxwxwwxxx/ghc,nathyong/microghc-ghc,ghc-android/ghc,gridaphobe/ghc,sgillespie/ghc,gcampax/ghc,fmthoma/ghc,forked-upstream-packages-for-ghcjs/ghc,elieux/ghc,ml9951/ghc,elieux/ghc,urbanslug/ghc,vikraman/ghc,nkaretnikov/ghc,TomMD/ghc,wxwxwwxxx/ghc,GaloisInc/halvm-ghc,oldmanmike/ghc,tjakway/ghcjvm,forked-upstream-packages-for-ghcjs/ghc,mfine/ghc,snoyberg/ghc,vTurbine/ghc,gridaphobe/ghc,da-x/ghc,olsner/ghc,TomMD/ghc,mfine/ghc,TomMD/ghc,shlevy/ghc,nkaretnikov/ghc,fmthoma/ghc,elieux/ghc,da-x/ghc,fmthoma/ghc,bitemyapp/ghc,olsner/ghc,nushio3/ghc,mcschroeder/ghc,ezyang/ghc,green-haskell/ghc,siddhanathan/ghc,shlevy/ghc,anton-dessiatov/ghc,mettekou/ghc,vTurbine/ghc,GaloisInc/halvm-ghc,bitemyapp/ghc,tjakway/ghcjvm,siddhanathan/ghc,nathyong/microghc-ghc,snoyberg/ghc,vikraman/ghc,shlevy/ghc,olsner/ghc,urbanslug/ghc,nkaretnikov/ghc,nushio3/ghc,da-x/ghc,gridaphobe/ghc,snoyberg/ghc,AlexanderPankiv/ghc,mfine/ghc,tjakway/ghcjvm,siddhanathan/ghc,green-haskell/ghc,christiaanb/ghc,green-haskell/ghc,nkaretnikov/ghc,ml9951/ghc,olsner/ghc,gcampax/ghc,christiaanb/ghc,nathyong/microghc-ghc,GaloisInc/halvm-ghc,nushio3/ghc,sgillespie/ghc,ezyang/ghc,acowley/ghc,sdiehl/ghc,AlexanderPankiv/ghc,ml9951/ghc,mcschroeder/ghc,christiaanb/ghc,vikraman/ghc,anton-dessiatov/ghc,ezyang/ghc,sgillespie/ghc,elieux/ghc,vikraman/ghc,anton-dessiatov/ghc,vikraman/ghc,wxwxwwxxx/ghc,siddhanathan/ghc