when MAX_CONCURRENT_THREAD_NUMBER is not specified, tool will
automatically detect number of processor threads.
Fixes: https://bugzilla.tianocore.org/show_bug.cgi?id=775
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
(cherry picked from commit 2052cb675f
)