Runtime detection of available processor cores.
Detect the number of available cores and limit the thread allocation accordingly. On decoder side limit the number of threads to the max number of token partition. Core detetction works on Windows and Posix platforms, which define _SC_NPROCESSORS_ONLN or _SC_NPROC_ONLN. Change-Id: I76cbe37c18d3b8035e508b7a1795577674efc078