Fix perf of DateTime.Now on Unix
Fix perf of DateTime.Now on Unix

Profiling DateTime.Now on Unix shows that a lot of time is spent in GetPreviousAdjustmentRule and AdjustmentRule::Equals. Instead, it is safe to use ReferenceEquals, which increases the performance of DateTime.Now and other time zone operations on Unix.

jamesqo/coreclr,tijoytom/coreclr,yeaicc/coreclr,James-Ko/coreclr,poizan42/coreclr,poizan42/coreclr,pgavlin/coreclr,JosephTremoulet/coreclr,krytarowski/coreclr,rartemev/coreclr,yeaicc/coreclr,wateret/coreclr,JosephTremoulet/coreclr,krk/coreclr,JosephTremoulet/coreclr,gkhanna79/coreclr,kyulee1/coreclr,tijoytom/coreclr,cmckinsey/coreclr,ruben-ayrapetyan/coreclr,JosephTremoulet/coreclr,mskvortsov/coreclr,wtgodbe/coreclr,ruben-ayrapetyan/coreclr,poizan42/coreclr,tijoytom/coreclr,mmitche/coreclr,cmckinsey/coreclr,YongseopKim/coreclr,jamesqo/coreclr,ragmani/coreclr,ragmani/coreclr,kyulee1/coreclr,pgavlin/coreclr,poizan42/coreclr,mmitche/coreclr,JonHanna/coreclr,yizhang82/coreclr,poizan42/coreclr,cshung/coreclr,qiudesong/coreclr,JonHanna/coreclr,cshung/coreclr,mmitche/coreclr,AlexGhiondea/coreclr,botaberg/coreclr,cmckinsey/coreclr,dpodder/coreclr,mmitche/coreclr,yeaicc/coreclr,qiudesong/coreclr,YongseopKim/coreclr,krk/coreclr,JonHanna/coreclr,James-Ko/coreclr,parjong/coreclr,yeaicc/coreclr,dpodder/coreclr,russellhadley/coreclr,wtgodbe/coreclr,jamesqo/coreclr,James-Ko/coreclr,YongseopKim/coreclr,qiudesong/coreclr,AlexGhiondea/coreclr,krytarowski/coreclr,cydhaselton/coreclr,YongseopKim/coreclr,AlexGhiondea/coreclr,alexperovich/coreclr,AlexGhiondea/coreclr,dpodder/coreclr,qiudesong/coreclr,alexperovich/coreclr,hseok-oh/coreclr,gkhanna79/coreclr,cydhaselton/coreclr,rartemev/coreclr,alexperovich/coreclr,krk/coreclr,russellhadley/coreclr,sagood/coreclr,wtgodbe/coreclr,krytarowski/coreclr,mmitche/coreclr,alexperovich/coreclr,wtgodbe/coreclr,sagood/coreclr,James-Ko/coreclr,yizhang82/coreclr,wateret/coreclr,rartemev/coreclr,wtgodbe/coreclr,cshung/coreclr,mskvortsov/coreclr,JosephTremoulet/coreclr,wateret/coreclr,wateret/coreclr,hseok-oh/coreclr,pgavlin/coreclr,alexperovich/coreclr,pgavlin/coreclr,kyulee1/coreclr,tijoytom/coreclr,hseok-oh/coreclr,krytarowski/coreclr,yeaicc/coreclr,yeaicc/coreclr,sagood/coreclr,AlexGhiondea/coreclr,ruben-ayrapetyan/coreclr,cmckinsey/coreclr,yizhang82/coreclr,qiudesong/coreclr,ragmani/coreclr,hseok-oh/coreclr,pgavlin/coreclr,botaberg/coreclr,JonHanna/coreclr,cshung/coreclr,cshung/coreclr,JonHanna/coreclr,James-Ko/coreclr,botaberg/coreclr,gkhanna79/coreclr,tijoytom/coreclr,rartemev/coreclr,russellhadley/coreclr,wateret/coreclr,mskvortsov/coreclr,yizhang82/coreclr,AlexGhiondea/coreclr,botaberg/coreclr,tijoytom/coreclr,gkhanna79/coreclr,jamesqo/coreclr,wtgodbe/coreclr,poizan42/coreclr,mmitche/coreclr,parjong/coreclr,hseok-oh/coreclr,dpodder/coreclr,krk/coreclr,cmckinsey/coreclr,JonHanna/coreclr,jamesqo/coreclr,yizhang82/coreclr,mskvortsov/coreclr,parjong/coreclr,cydhaselton/coreclr,russellhadley/coreclr,sagood/coreclr,yeaicc/coreclr,ruben-ayrapetyan/coreclr,ruben-ayrapetyan/coreclr,wateret/coreclr,cydhaselton/coreclr,cydhaselton/coreclr,cydhaselton/coreclr,sagood/coreclr,sagood/coreclr,ragmani/coreclr,cmckinsey/coreclr,ragmani/coreclr,alexperovich/coreclr,kyulee1/coreclr,ruben-ayrapetyan/coreclr,James-Ko/coreclr,hseok-oh/coreclr,YongseopKim/coreclr,russellhadley/coreclr,kyulee1/coreclr,parjong/coreclr,krk/coreclr,krytarowski/coreclr,krk/coreclr,parjong/coreclr,JosephTremoulet/coreclr,qiudesong/coreclr,mskvortsov/coreclr,ragmani/coreclr,mskvortsov/coreclr,YongseopKim/coreclr,cshung/coreclr,kyulee1/coreclr,pgavlin/coreclr,gkhanna79/coreclr,gkhanna79/coreclr,dpodder/coreclr,botaberg/coreclr,jamesqo/coreclr,yizhang82/coreclr,rartemev/coreclr,krytarowski/coreclr,rartemev/coreclr,dpodder/coreclr,cmckinsey/coreclr,parjong/coreclr,russellhadley/coreclr,botaberg/coreclr