users-guide: Note change in LLVM support policy
users-guide: Note change in LLVM support policy

tjakway/ghcjvm,olsner/ghc,vikraman/ghc,vTurbine/ghc,sgillespie/ghc,vikraman/ghc,vikraman/ghc,ezyang/ghc,snoyberg/ghc,sgillespie/ghc,ezyang/ghc,mettekou/ghc,olsner/ghc,sdiehl/ghc,olsner/ghc,mettekou/ghc,vTurbine/ghc,mettekou/ghc,snoyberg/ghc,sgillespie/ghc,sdiehl/ghc,vTurbine/ghc,snoyberg/ghc,vikraman/ghc,sdiehl/ghc,vTurbine/ghc,shlevy/ghc,snoyberg/ghc,tjakway/ghcjvm,mettekou/ghc,sdiehl/ghc,mettekou/ghc,shlevy/ghc,shlevy/ghc,sgillespie/ghc,mettekou/ghc,ezyang/ghc,tjakway/ghcjvm,tjakway/ghcjvm,ezyang/ghc,tjakway/ghcjvm,tjakway/ghcjvm,tjakway/ghcjvm,shlevy/ghc,sgillespie/ghc,ezyang/ghc,shlevy/ghc,sgillespie/ghc,sdiehl/ghc,vTurbine/ghc,shlevy/ghc,vTurbine/ghc,snoyberg/ghc,ezyang/ghc,sdiehl/ghc,snoyberg/ghc,vikraman/ghc,olsner/ghc,sdiehl/ghc,sgillespie/ghc,olsner/ghc,olsner/ghc,snoyberg/ghc,shlevy/ghc,ezyang/ghc,mettekou/ghc,vTurbine/ghc,vikraman/ghc,olsner/ghc,vikraman/ghc