Clamp -O flag to beween 0 and 2
Clamp -O flag to beween 0 and 2

Fixes Trac #1272


GaloisInc/halvm-ghc,gridaphobe/ghc,ilyasergey/GHC-XAppFix,nkaretnikov/ghc,ml9951/ghc,siddhanathan/ghc,siddhanathan/ghc,mettekou/ghc,snoyberg/ghc,holzensp/ghc,forked-upstream-packages-for-ghcjs/ghc,nathyong/microghc-ghc,holzensp/ghc,ml9951/ghc,oldmanmike/ghc,nomeata/ghc,bitemyapp/ghc,frantisekfarka/ghc-dsi,forked-upstream-packages-for-ghcjs/ghc,shlevy/ghc,lukexi/ghc-7.8-arm64,anton-dessiatov/ghc,green-haskell/ghc,forked-upstream-packages-for-ghcjs/ghc,TomMD/ghc,ezyang/ghc,da-x/ghc,da-x/ghc,snoyberg/ghc,AlexanderPankiv/ghc,christiaanb/ghc,ekmett/ghc,GaloisInc/halvm-ghc,TomMD/ghc,tibbe/ghc,nushio3/ghc,AlexanderPankiv/ghc,nushio3/ghc,holzensp/ghc,nkaretnikov/ghc,nathyong/microghc-ghc,ezyang/ghc,frantisekfarka/ghc-dsi,olsner/ghc,bitemyapp/ghc,sdiehl/ghc,siddhanathan/ghc,fmthoma/ghc,siddhanathan/ghc,jstolarek/ghc,acowley/ghc,nkaretnikov/ghc,gcampax/ghc,vikraman/ghc,nathyong/microghc-ghc,mettekou/ghc,lukexi/ghc-7.8-arm64,ryantm/ghc,mfine/ghc,nushio3/ghc,bitemyapp/ghc,hferreiro/replay,ekmett/ghc,lukexi/ghc,sgillespie/ghc,ghc-android/ghc,vikraman/ghc,vTurbine/ghc,lukexi/ghc-7.8-arm64,olsner/ghc,christiaanb/ghc,TomMD/ghc,acowley/ghc,mettekou/ghc,mettekou/ghc,acowley/ghc,vikraman/ghc,sdiehl/ghc,anton-dessiatov/ghc,gcampax/ghc,tibbe/ghc,anton-dessiatov/ghc,ghc-android/ghc,gridaphobe/ghc,sgillespie/ghc,da-x/ghc,ghc-android/ghc,ilyasergey/GHC-XAppFix,hferreiro/replay,elieux/ghc,ekmett/ghc,ml9951/ghc,nomeata/ghc,ghc-android/ghc,tjakway/ghcjvm,nathyong/microghc-ghc,acowley/ghc,shlevy/ghc,ml9951/ghc,nkaretnikov/ghc,ml9951/ghc,da-x/ghc,gridaphobe/ghc,snoyberg/ghc,frantisekfarka/ghc-dsi,sgillespie/ghc,tjakway/ghcjvm,anton-dessiatov/ghc,fmthoma/ghc,mcschroeder/ghc,frantisekfarka/ghc-dsi,forked-upstream-packages-for-ghcjs/ghc,sgillespie/ghc,gridaphobe/ghc,oldmanmike/ghc,ezyang/ghc,da-x/ghc,tjakway/ghcjvm,shlevy/ghc,oldmanmike/ghc,vTurbine/ghc,mettekou/ghc,hferreiro/replay,sdiehl/ghc,GaloisInc/halvm-ghc,fmthoma/ghc,anton-dessiatov/ghc,nkaretnikov/ghc,snoyberg/ghc,sgillespie/ghc,vTurbine/ghc,spacekitteh/smcghc,olsner/ghc,ezyang/ghc,ekmett/ghc,mfine/ghc,bitemyapp/ghc,AlexanderPankiv/ghc,green-haskell/ghc,snoyberg/ghc,ghc-android/ghc,GaloisInc/halvm-ghc,oldmanmike/ghc,mcschroeder/ghc,nomeata/ghc,da-x/ghc,snoyberg/ghc,forked-upstream-packages-for-ghcjs/ghc,urbanslug/ghc,gridaphobe/ghc,lukexi/ghc-7.8-arm64,mfine/ghc,oldmanmike/ghc,ml9951/ghc,vTurbine/ghc,fmthoma/ghc,gridaphobe/ghc,ezyang/ghc,GaloisInc/halvm-ghc,nkaretnikov/ghc,fmthoma/ghc,mfine/ghc,nushio3/ghc,bitemyapp/ghc,vikraman/ghc,TomMD/ghc,nushio3/ghc,holzensp/ghc,wxwxwwxxx/ghc,jstolarek/ghc,mcschroeder/ghc,lukexi/ghc,TomMD/ghc,tibbe/ghc,anton-dessiatov/ghc,AlexanderPankiv/ghc,spacekitteh/smcghc,tjakway/ghcjvm,christiaanb/ghc,spacekitteh/smcghc,GaloisInc/halvm-ghc,tjakway/ghcjvm,mcschroeder/ghc,TomMD/ghc,acowley/ghc,nomeata/ghc,ml9951/ghc,mfine/ghc,nkaretnikov/ghc,wxwxwwxxx/ghc,AlexanderPankiv/ghc,jstolarek/ghc,ilyasergey/GHC-XAppFix,green-haskell/ghc,hferreiro/replay,siddhanathan/ghc,fmthoma/ghc,ml9951/ghc,urbanslug/ghc,green-haskell/ghc,nathyong/microghc-ghc,gcampax/ghc,vikraman/ghc,urbanslug/ghc,ghc-android/ghc,spacekitteh/smcghc,olsner/ghc,lukexi/ghc,sdiehl/ghc,forked-upstream-packages-for-ghcjs/ghc,mfine/ghc,shlevy/ghc,vikraman/ghc,mcschroeder/ghc,elieux/ghc,ilyasergey/GHC-XAppFix,GaloisInc/halvm-ghc,mettekou/ghc,holzensp/ghc,hferreiro/replay,elieux/ghc,AlexanderPankiv/ghc,jstolarek/ghc,vTurbine/ghc,wxwxwwxxx/ghc,forked-upstream-packages-for-ghcjs/ghc,christiaanb/ghc,TomMD/ghc,vikraman/ghc,siddhanathan/ghc,sgillespie/ghc,acowley/ghc,ghc-android/ghc,shlevy/ghc,ryantm/ghc,sdiehl/ghc,wxwxwwxxx/ghc,mcmaniac/ghc,nathyong/microghc-ghc,christiaanb/ghc,ryantm/ghc,mcschroeder/ghc,ezyang/ghc,wxwxwwxxx/ghc,nathyong/microghc-ghc,acowley/ghc,siddhanathan/ghc,shlevy/ghc,tjakway/ghcjvm,shlevy/ghc,nushio3/ghc,AlexanderPankiv/ghc,nushio3/ghc,snoyberg/ghc,olsner/ghc,urbanslug/ghc,mcschroeder/ghc,oldmanmike/ghc,olsner/ghc,mcmaniac/ghc,lukexi/ghc,gcampax/ghc,christiaanb/ghc,olsner/ghc,mcmaniac/ghc,christiaanb/ghc,elieux/ghc,ryantm/ghc,ryantm/ghc,mfine/ghc,gcampax/ghc,jstolarek/ghc,ekmett/ghc,elieux/ghc,spacekitteh/smcghc,sdiehl/ghc,gridaphobe/ghc,vTurbine/ghc,urbanslug/ghc,oldmanmike/ghc,gcampax/ghc,green-haskell/ghc,urbanslug/ghc,da-x/ghc,sdiehl/ghc,mcmaniac/ghc,urbanslug/ghc,hferreiro/replay,elieux/ghc,elieux/ghc,lukexi/ghc,hferreiro/replay,frantisekfarka/ghc-dsi,mcmaniac/ghc,wxwxwwxxx/ghc,nomeata/ghc,vTurbine/ghc,fmthoma/ghc,gcampax/ghc,tibbe/ghc,sgillespie/ghc,ezyang/ghc,wxwxwwxxx/ghc,tibbe/ghc,lukexi/ghc-7.8-arm64,mettekou/ghc,anton-dessiatov/ghc,tjakway/ghcjvm