Resolve GCC build error, where #pragma pack(push[, id], <n>) is not supported.

signed off by: jiewen.yao@intel.com


git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/MdePkg@14691 6f19259b-4bc3-4df7-8a09-765794883524