Fix globalRegMaybe for unregisterised build.
Fix globalRegMaybe for unregisterised build.

In commit 83a003f globalRegMaybe will be called but panics
for unregisterised compilers.

In an unregisterised compiler there are no global registers
so always return `Nothing`.

Fixes #9055.

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