implement ARMv6/7 specific xchg function
implement ARMv6/7 specific xchg function

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