Make rebindable if-then-else a little more permissive
Make rebindable if-then-else a little more permissive

See Note [Rebindable syntax for if].  Fixes Trac #4798.
Thanks to Nils Schweinsberg <mail@n-sch.de>

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