Remove unneeded compatibility with LLVM < 3.6
Remove unneeded compatibility with LLVM < 3.6

Since GHC requires at least LLVM 3.6, some of the special cases (for,
e.g., LLVM 2.8 or 2.9) in the LLVM CodeGen can be simply removed.

Reviewed By: rwbarton, austin

Differential Revision: https://phabricator.haskell.org/D884

GHC Trac Issues: #10074

wxwxwwxxx/ghc,AlexanderPankiv/ghc,AlexanderPankiv/ghc,ezyang/ghc,sdiehl/ghc,vTurbine/ghc,mcschroeder/ghc,snoyberg/ghc,TomMD/ghc,da-x/ghc,wxwxwwxxx/ghc,vikraman/ghc,olsner/ghc,siddhanathan/ghc,mfine/ghc,TomMD/ghc,TomMD/ghc,GaloisInc/halvm-ghc,snoyberg/ghc,mfine/ghc,sdiehl/ghc,nushio3/ghc,mettekou/ghc,urbanslug/ghc,vikraman/ghc,ezyang/ghc,sgillespie/ghc,gridaphobe/ghc,ghc-android/ghc,ezyang/ghc,wxwxwwxxx/ghc,oldmanmike/ghc,mfine/ghc,anton-dessiatov/ghc,gridaphobe/ghc,fmthoma/ghc,urbanslug/ghc,nkaretnikov/ghc,ml9951/ghc,vikraman/ghc,sdiehl/ghc,fmthoma/ghc,acowley/ghc,urbanslug/ghc,mettekou/ghc,anton-dessiatov/ghc,vikraman/ghc,gridaphobe/ghc,olsner/ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,vTurbine/ghc,urbanslug/ghc,acowley/ghc,shlevy/ghc,elieux/ghc,mettekou/ghc,oldmanmike/ghc,ezyang/ghc,acowley/ghc,mcschroeder/ghc,nushio3/ghc,vTurbine/ghc,nushio3/ghc,anton-dessiatov/ghc,fmthoma/ghc,nkaretnikov/ghc,ml9951/ghc,AlexanderPankiv/ghc,AlexanderPankiv/ghc,da-x/ghc,snoyberg/ghc,oldmanmike/ghc,fmthoma/ghc,acowley/ghc,sgillespie/ghc,shlevy/ghc,TomMD/ghc,snoyberg/ghc,ghc-android/ghc,nkaretnikov/ghc,mfine/ghc,GaloisInc/halvm-ghc,gridaphobe/ghc,snoyberg/ghc,AlexanderPankiv/ghc,shlevy/ghc,urbanslug/ghc,sgillespie/ghc,urbanslug/ghc,elieux/ghc,GaloisInc/halvm-ghc,shlevy/ghc,mettekou/ghc,sgillespie/ghc,anton-dessiatov/ghc,wxwxwwxxx/ghc,mfine/ghc,mettekou/ghc,da-x/ghc,mcschroeder/ghc,vikraman/ghc,fmthoma/ghc,ml9951/ghc,olsner/ghc,vTurbine/ghc,sgillespie/ghc,vTurbine/ghc,snoyberg/ghc,sdiehl/ghc,elieux/ghc,acowley/ghc,olsner/ghc,ml9951/ghc,mcschroeder/ghc,wxwxwwxxx/ghc,sdiehl/ghc,GaloisInc/halvm-ghc,olsner/ghc,siddhanathan/ghc,shlevy/ghc,fmthoma/ghc,AlexanderPankiv/ghc,da-x/ghc,sgillespie/ghc,anton-dessiatov/ghc,nkaretnikov/ghc,ml9951/ghc,mfine/ghc,tjakway/ghcjvm,oldmanmike/ghc,TomMD/ghc,tjakway/ghcjvm,nushio3/ghc,snoyberg/ghc,sgillespie/ghc,nushio3/ghc,ezyang/ghc,acowley/ghc,oldmanmike/ghc,vikraman/ghc,vikraman/ghc,tjakway/ghcjvm,ml9951/ghc,tjakway/ghcjvm,mcschroeder/ghc,ghc-android/ghc,ghc-android/ghc,nkaretnikov/ghc,sdiehl/ghc,ml9951/ghc,wxwxwwxxx/ghc,fmthoma/ghc,shlevy/ghc,tjakway/ghcjvm,AlexanderPankiv/ghc,ml9951/ghc,siddhanathan/ghc,acowley/ghc,TomMD/ghc,ezyang/ghc,elieux/ghc,elieux/ghc,nkaretnikov/ghc,elieux/ghc,tjakway/ghcjvm,anton-dessiatov/ghc,mettekou/ghc,olsner/ghc,gridaphobe/ghc,tjakway/ghcjvm,elieux/ghc,olsner/ghc,anton-dessiatov/ghc,ghc-android/ghc,siddhanathan/ghc,gridaphobe/ghc,da-x/ghc,oldmanmike/ghc,oldmanmike/ghc,GaloisInc/halvm-ghc,vTurbine/ghc,ghc-android/ghc,nkaretnikov/ghc,da-x/ghc,siddhanathan/ghc,wxwxwwxxx/ghc,siddhanathan/ghc,vTurbine/ghc,mfine/ghc,da-x/ghc,nushio3/ghc,sdiehl/ghc,urbanslug/ghc,gridaphobe/ghc,siddhanathan/ghc,ghc-android/ghc,ezyang/ghc,TomMD/ghc,shlevy/ghc,mcschroeder/ghc,mcschroeder/ghc,nushio3/ghc,mettekou/ghc