Update unpack format to be portable.
Update unpack format to be portable.

Reviewed-by: Andrew Fish <afish@apple.com>
Signed-off-by: Yingke Liu <yingke.d.liu@intel.com>

git-svn-id: 9f565f781a21d49e5eb65309b10d68363fc24972@2637 c2973edb-eda0-4c78-bc6a-9341b269661f

tianocore/buildtools-BaseTools,tianocore/buildtools-BaseTools,bitcrystal/buildtools-BaseTools,bitcrystal/buildtools-BaseTools,tianocore/buildtools-BaseTools,bitcrystal/buildtools-BaseTools,bitcrystal/buildtools-BaseTools,bitcrystal/buildtools-BaseTools,tianocore/buildtools-BaseTools,tianocore/buildtools-BaseTools