Use clock_gettime(CLOCK_REALTIME) in DateTime.UtcNow (#9772)
Use clock_gettime(CLOCK_REALTIME) in DateTime.UtcNow (#9772)

gettimeofday() is currently used in DateTime.UtcNow.  Depending on the system, it may have accuracy and precision in line with either clock_gettime(CLOCK_REALTIME) or clock_gettime(CLOCK_REALTIME_COARSE), but in returning its data it's necessarily limited by struct timeval's tv_usec field (microseconds), whereas clock_gettime uses struct timespec which has tv_nsec (nanoseconds).  This commit switches to use clock_gettime(CLOCK_REALTIME) to gain the additional precision (though the FILETIME through which the data is returned only supports 100-nsec precision).  On my machine, there was no measurable impact to throughput.
ruben-ayrapetyan/coreclr,russellhadley/coreclr,AlexGhiondea/coreclr,botaberg/coreclr,wateret/coreclr,wateret/coreclr,ragmani/coreclr,qiudesong/coreclr,kyulee1/coreclr,qiudesong/coreclr,James-Ko/coreclr,cmckinsey/coreclr,cydhaselton/coreclr,ragmani/coreclr,russellhadley/coreclr,cshung/coreclr,wtgodbe/coreclr,rartemev/coreclr,cmckinsey/coreclr,sagood/coreclr,JonHanna/coreclr,jamesqo/coreclr,rartemev/coreclr,mskvortsov/coreclr,tijoytom/coreclr,krk/coreclr,wtgodbe/coreclr,wateret/coreclr,pgavlin/coreclr,cmckinsey/coreclr,pgavlin/coreclr,ragmani/coreclr,russellhadley/coreclr,jamesqo/coreclr,krk/coreclr,mmitche/coreclr,gkhanna79/coreclr,qiudesong/coreclr,yizhang82/coreclr,cshung/coreclr,cmckinsey/coreclr,yizhang82/coreclr,tijoytom/coreclr,mmitche/coreclr,yeaicc/coreclr,yeaicc/coreclr,parjong/coreclr,alexperovich/coreclr,tijoytom/coreclr,sagood/coreclr,hseok-oh/coreclr,yeaicc/coreclr,botaberg/coreclr,rartemev/coreclr,wtgodbe/coreclr,yeaicc/coreclr,krytarowski/coreclr,gkhanna79/coreclr,kyulee1/coreclr,poizan42/coreclr,cydhaselton/coreclr,JonHanna/coreclr,tijoytom/coreclr,James-Ko/coreclr,sjsinju/coreclr,krytarowski/coreclr,kyulee1/coreclr,yizhang82/coreclr,parjong/coreclr,AlexGhiondea/coreclr,hseok-oh/coreclr,pgavlin/coreclr,qiudesong/coreclr,jamesqo/coreclr,tijoytom/coreclr,botaberg/coreclr,kyulee1/coreclr,cmckinsey/coreclr,AlexGhiondea/coreclr,pgavlin/coreclr,cshung/coreclr,dpodder/coreclr,pgavlin/coreclr,YongseopKim/coreclr,cshung/coreclr,mmitche/coreclr,russellhadley/coreclr,JonHanna/coreclr,AlexGhiondea/coreclr,JonHanna/coreclr,mmitche/coreclr,cmckinsey/coreclr,tijoytom/coreclr,poizan42/coreclr,jamesqo/coreclr,kyulee1/coreclr,hseok-oh/coreclr,rartemev/coreclr,jamesqo/coreclr,dpodder/coreclr,botaberg/coreclr,wateret/coreclr,krytarowski/coreclr,JonHanna/coreclr,poizan42/coreclr,alexperovich/coreclr,sagood/coreclr,alexperovich/coreclr,dpodder/coreclr,cydhaselton/coreclr,ruben-ayrapetyan/coreclr,wateret/coreclr,ruben-ayrapetyan/coreclr,wtgodbe/coreclr,wateret/coreclr,krk/coreclr,sjsinju/coreclr,JosephTremoulet/coreclr,sjsinju/coreclr,AlexGhiondea/coreclr,krytarowski/coreclr,gkhanna79/coreclr,JosephTremoulet/coreclr,botaberg/coreclr,JonHanna/coreclr,ragmani/coreclr,cshung/coreclr,sjsinju/coreclr,mskvortsov/coreclr,krytarowski/coreclr,jamesqo/coreclr,sagood/coreclr,alexperovich/coreclr,pgavlin/coreclr,russellhadley/coreclr,mskvortsov/coreclr,kyulee1/coreclr,parjong/coreclr,sagood/coreclr,James-Ko/coreclr,poizan42/coreclr,JosephTremoulet/coreclr,cydhaselton/coreclr,yeaicc/coreclr,mmitche/coreclr,krytarowski/coreclr,yeaicc/coreclr,JosephTremoulet/coreclr,AlexGhiondea/coreclr,mskvortsov/coreclr,James-Ko/coreclr,JosephTremoulet/coreclr,YongseopKim/coreclr,gkhanna79/coreclr,mmitche/coreclr,yizhang82/coreclr,yeaicc/coreclr,dpodder/coreclr,qiudesong/coreclr,parjong/coreclr,hseok-oh/coreclr,alexperovich/coreclr,YongseopKim/coreclr,krk/coreclr,russellhadley/coreclr,rartemev/coreclr,ragmani/coreclr,krk/coreclr,krk/coreclr,dpodder/coreclr,sagood/coreclr,yizhang82/coreclr,alexperovich/coreclr,cydhaselton/coreclr,botaberg/coreclr,ruben-ayrapetyan/coreclr,cydhaselton/coreclr,parjong/coreclr,gkhanna79/coreclr,gkhanna79/coreclr,sjsinju/coreclr,mskvortsov/coreclr,ruben-ayrapetyan/coreclr,dpodder/coreclr,parjong/coreclr,wtgodbe/coreclr,James-Ko/coreclr,mskvortsov/coreclr,wtgodbe/coreclr,qiudesong/coreclr,YongseopKim/coreclr,JosephTremoulet/coreclr,sjsinju/coreclr,poizan42/coreclr,ruben-ayrapetyan/coreclr,YongseopKim/coreclr,James-Ko/coreclr,ragmani/coreclr,cshung/coreclr,hseok-oh/coreclr,yizhang82/coreclr,rartemev/coreclr,cmckinsey/coreclr,hseok-oh/coreclr,YongseopKim/coreclr,poizan42/coreclr