Previously with the help from gcc, __builtin_return_address(0) is
used as the guest entry address, but it can't work well with gcc 7.3
and leads to the guest unable to return to UEFI correctly.
Let's get it explicitly.
Signed-off-by: Jack Ren <jack.ren@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>