Remove mask of SIGCHLD
Remove mask of SIGCHLD

When a .NET Core program invoked a process that invoked its own child,
the masking of SIGCHLD prevented the process from recognizing its child
had exited, which some processes require. This caused the .NET Core app
to hang in certain internal scenarios.

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