Port coreclr#9241 to CoreRT (#4156)
Port coreclr#9241 to CoreRT (#4156)

Port of https://github.com/dotnet/coreclr/pull/9241 to CoreRT. This fixes an issue where the segment mapping table can accidentally get decommitted when running under extremely high memory pressure.
gregkalapos/corert,shrah/corert,yizhang82/corert,shrah/corert,yizhang82/corert,gregkalapos/corert,gregkalapos/corert,yizhang82/corert,shrah/corert,gregkalapos/corert,yizhang82/corert,shrah/corert