[yaml2obj] [MachO] Fill Segment and Section data

This fills section data with 0xDEADBEEF and segment data not inside a section with 0xBAADDA7A. This results in yaml2obj generating a matching size object file. Any additional bytes in the file are zero'd.

This is a starting point for populating the remaining segment data, and provides a hex viewable file that you can easily see the missing data in.

llvm-svn: 270286