Fix OverflowException in b115557.cs GC test on systems with fewer than four processors/cores
Fix OverflowException in b115557.cs GC test on systems with fewer than four processors/cores

_allocPerThreadMB/2 can be larger than what fits into byte (because it's based on the number of processors/cores),
resulting in an OverflowException on those systems.

jamesqo/coreclr,poizan42/coreclr,rartemev/coreclr,JosephTremoulet/coreclr,ktos/coreclr,blackdwarf/coreclr,yizhang82/coreclr,yeaicc/coreclr,Dmitry-Me/coreclr,kyulee1/coreclr,tijoytom/coreclr,manu-silicon/coreclr,manu-silicon/coreclr,LLITCHEV/coreclr,manu-silicon/coreclr,krk/coreclr,josteink/coreclr,YongseopKim/coreclr,manu-silicon/coreclr,ramarag/coreclr,bitcrazed/coreclr,jamesqo/coreclr,taylorjonl/coreclr,mmitche/coreclr,ramarag/coreclr,Dmitry-Me/coreclr,cmckinsey/coreclr,dpodder/coreclr,mskvortsov/coreclr,blackdwarf/coreclr,schellap/coreclr,krytarowski/coreclr,naamunds/coreclr,Lucrecious/coreclr,poizan42/coreclr,sperling/coreclr,Godin/coreclr,Lucrecious/coreclr,bartonjs/coreclr,qiudesong/coreclr,tijoytom/coreclr,roncain/coreclr,cydhaselton/coreclr,ktos/coreclr,andschwa/coreclr,AlexGhiondea/coreclr,andschwa/coreclr,roncain/coreclr,josteink/coreclr,sejongoh/coreclr,sjsinju/coreclr,dpodder/coreclr,benpye/coreclr,shahid-pk/coreclr,botaberg/coreclr,tijoytom/coreclr,dpodder/coreclr,mocsy/coreclr,bartdesmet/coreclr,KrzysztofCwalina/coreclr,ZhichengZhu/coreclr,mmitche/coreclr,ruben-ayrapetyan/coreclr,gkhanna79/coreclr,kyulee1/coreclr,krytarowski/coreclr,roncain/coreclr,kyulee1/coreclr,dasMulli/coreclr,mokchhya/coreclr,wateret/coreclr,andschwa/coreclr,krytarowski/coreclr,SlavaRa/coreclr,ktos/coreclr,cshung/coreclr,jhendrixMSFT/coreclr,geertdoornbos/coreclr,poizan42/coreclr,neurospeech/coreclr,wkchoy74/coreclr,stormleoxia/coreclr,SlavaRa/coreclr,vinnyrom/coreclr,naamunds/coreclr,schellap/coreclr,qiudesong/coreclr,JosephTremoulet/coreclr,blackdwarf/coreclr,yizhang82/coreclr,alexperovich/coreclr,naamunds/coreclr,manu-silicon/coreclr,cmckinsey/coreclr,James-Ko/coreclr,cmckinsey/coreclr,ZhichengZhu/coreclr,mocsy/coreclr,mskvortsov/coreclr,kyulee1/coreclr,geertdoornbos/coreclr,wtgodbe/coreclr,russellhadley/coreclr,swgillespie/coreclr,cmckinsey/coreclr,ragmani/coreclr,jhendrixMSFT/coreclr,ZhichengZhu/coreclr,yizhang82/coreclr,parjong/coreclr,JosephTremoulet/coreclr,mocsy/coreclr,cmckinsey/coreclr,bitcrazed/coreclr,martinwoodward/coreclr,cydhaselton/coreclr,mocsy/coreclr,manu-silicon/coreclr,James-Ko/coreclr,wtgodbe/coreclr,ruben-ayrapetyan/coreclr,bartdesmet/coreclr,dasMulli/coreclr,geertdoornbos/coreclr,alexperovich/coreclr,bartonjs/coreclr,bartonjs/coreclr,yeaicc/coreclr,tijoytom/coreclr,YongseopKim/coreclr,shahid-pk/coreclr,dasMulli/coreclr,tijoytom/coreclr,naamunds/coreclr,wtgodbe/coreclr,parjong/coreclr,LLITCHEV/coreclr,jamesqo/coreclr,kyulee1/coreclr,Lucrecious/coreclr,mskvortsov/coreclr,martinwoodward/coreclr,JosephTremoulet/coreclr,gkhanna79/coreclr,vinnyrom/coreclr,sjsinju/coreclr,Dmitry-Me/coreclr,alexperovich/coreclr,roncain/coreclr,krk/coreclr,geertdoornbos/coreclr,bitcrazed/coreclr,JonHanna/coreclr,stormleoxia/coreclr,Lucrecious/coreclr,KrzysztofCwalina/coreclr,cshung/coreclr,jamesqo/coreclr,russellhadley/coreclr,JonHanna/coreclr,vinnyrom/coreclr,alexperovich/coreclr,manu-silicon/coreclr,Dmitry-Me/coreclr,ragmani/coreclr,neurospeech/coreclr,qiudesong/coreclr,rartemev/coreclr,stormleoxia/coreclr,swgillespie/coreclr,wateret/coreclr,jhendrixMSFT/coreclr,jamesqo/coreclr,pgavlin/coreclr,JonHanna/coreclr,sejongoh/coreclr,ruben-ayrapetyan/coreclr,taylorjonl/coreclr,sagood/coreclr,taylorjonl/coreclr,taylorjonl/coreclr,dpodder/coreclr,Lucrecious/coreclr,tijoytom/coreclr,bitcrazed/coreclr,yeaicc/coreclr,AlexGhiondea/coreclr,poizan42/coreclr,shahid-pk/coreclr,JosephTremoulet/coreclr,chuck-mitchell/coreclr,sperling/coreclr,hseok-oh/coreclr,botaberg/coreclr,James-Ko/coreclr,gkhanna79/coreclr,chuck-mitchell/coreclr,bartdesmet/coreclr,dasMulli/coreclr,cydhaselton/coreclr,wateret/coreclr,shahid-pk/coreclr,yeaicc/coreclr,wkchoy74/coreclr,yeaicc/coreclr,sejongoh/coreclr,jhendrixMSFT/coreclr,taylorjonl/coreclr,Lucrecious/coreclr,sejongoh/coreclr,ktos/coreclr,vinnyrom/coreclr,krk/coreclr,ramarag/coreclr,sagood/coreclr,russellhadley/coreclr,Dmitry-Me/coreclr,bitcrazed/coreclr,wkchoy74/coreclr,cydhaselton/coreclr,roncain/coreclr,parjong/coreclr,neurospeech/coreclr,ragmani/coreclr,LLITCHEV/coreclr,sagood/coreclr,Lucrecious/coreclr,Godin/coreclr,yizhang82/coreclr,Godin/coreclr,pgavlin/coreclr,bitcrazed/coreclr,mmitche/coreclr,shahid-pk/coreclr,LLITCHEV/coreclr,hseok-oh/coreclr,YongseopKim/coreclr,ruben-ayrapetyan/coreclr,blackdwarf/coreclr,James-Ko/coreclr,schellap/coreclr,martinwoodward/coreclr,naamunds/coreclr,vinnyrom/coreclr,sperling/coreclr,cydhaselton/coreclr,krk/coreclr,krytarowski/coreclr,cshung/coreclr,mokchhya/coreclr,mskvortsov/coreclr,dasMulli/coreclr,yeaicc/coreclr,ramarag/coreclr,mokchhya/coreclr,cydhaselton/coreclr,SlavaRa/coreclr,qiudesong/coreclr,sejongoh/coreclr,bartonjs/coreclr,blackdwarf/coreclr,wtgodbe/coreclr,pgavlin/coreclr,chuck-mitchell/coreclr,josteink/coreclr,chuck-mitchell/coreclr,chuck-mitchell/coreclr,sperling/coreclr,geertdoornbos/coreclr,ramarag/coreclr,gkhanna79/coreclr,andschwa/coreclr,LLITCHEV/coreclr,sagood/coreclr,dasMulli/coreclr,mskvortsov/coreclr,SlavaRa/coreclr,neurospeech/coreclr,schellap/co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