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: https://svn.code.sf.net/p/edk2-buildtools/code/trunk/BaseTools@2637 c2973edb-eda0-4c78-bc6a-9341b269661f
Fix a bug which report error if a correct FD contains a region with no region type followed by another region whose offset is an expression staring with a PCD.

Reviewed-by: Liming Gao <liming.gao@intel.com>
Signed-off-by: Yingke Liu <yingke.d.liu@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2-buildtools/code/trunk/BaseTools@2638 c2973edb-eda0-4c78-bc6a-9341b269661f