Tidy up tso->stackobj before calling threadStackUnderflow (#7636)
Tidy up tso->stackobj before calling threadStackUnderflow (#7636)

Fixes the following crash:

  internal error: threadStackUnderflow: not enough space for return values

when using STM.

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