In the PAL GetProcessTimes implement lpCreationTime using the current time returned...

In the PAL GetProcessTimes implement lpCreationTime using the current time returned by gettimeofday
This allows IBC profile data to record a meaningful time of when the training scenario was run.
Made EPOCH_DIFF a defined constant
Change calcTime to be an unsigned 64-bit integer
Change constants to units of 100NS instead of NS to avoid division and integer overflows.
Use the defined constants SECS_TO_100NS and USECS_TO_100NS when performing time calculations
Don't add a space after the Assembly arg when argc is zero

Commit migrated from https://github.com/dotnet/coreclr/commit/e7815dde1e3847841b260e700704da8f7b4f7a30