Adding out-of-process execution support to lli.

At this time only Unix-based systems are supported.  Windows has stubs and should re-route to the simulated mode.

Thanks to Sriram Murali for contributions to this patch.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191843 91177308-0d34-0410-b5e6-96231b3b80d8