Update UsingYourBuild.md
Update UsingYourBuild.md

Apparently it needs a PlatformTarget to be specified as well when targeting x64 architecture
yizhang82/coreclr,poizan42/coreclr,poizan42/coreclr,yizhang82/coreclr,yizhang82/coreclr,poizan42/coreclr,mmitche/coreclr,cshung/coreclr,yizhang82/coreclr,krk/coreclr,poizan42/coreclr,wtgodbe/coreclr,wtgodbe/coreclr,cshung/coreclr,poizan42/coreclr,ruben-ayrapetyan/coreclr,mmitche/coreclr,krk/coreclr,ruben-ayrapetyan/coreclr,ruben-ayrapetyan/coreclr,poizan42/coreclr,cshung/coreclr,yizhang82/coreclr,ruben-ayrapetyan/coreclr,ruben-ayrapetyan/coreclr,cshung/coreclr,krk/coreclr,mmitche/coreclr,mmitche/coreclr,krk/coreclr,cshung/coreclr,mmitche/coreclr,wtgodbe/coreclr,cshung/coreclr,mmitche/coreclr,yizhang82/coreclr,krk/coreclr,ruben-ayrapetyan/coreclr,wtgodbe/coreclr,wtgodbe/coreclr,wtgodbe/coreclr,krk/coreclr