RTS: fix xchg/cas fcns to invoke memory barrier on ARMv7 platform
RTS: fix xchg/cas fcns to invoke memory barrier on ARMv7 platform

This patch fixes RTS' xchg and cas functions. On ARMv7 it is recommended
to add memory barrier after using ldrex/strex for implementing atomic
lock or operation.

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