BaseTools: Fix Segmentation fault: 11 when build AppPkg with XCODE5

BaseTools: Fix Segmentation fault: 11 when build AppPkg with XCODE5

it is a bug in mtoc setting the size of the debug directory entry to
the size of the .debug section, not the size of the
EFI_IMAGE_DEBUG_DIRECTORY_ENTRY. It was causing a loop to iterate and
get bogus EFI_IMAGE_DEBUG_DIRECTORY_ENTRY data and pass that to
memset() and boom.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Andrew Fish <afish@apple.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>