swift234

[swift-c++-bench] Modify ObjInst so that like the swift benchmark we use mach_absolute_time inside the program to do the timing of the routine.

One might wonder, why not just not use mach_absolute_time in the swift program
instead. The reason why is that using mach_absolute_time in this manner filters
out process startup noise as well as anything in the program we do not want to
time.

Swift SVN r12793