[yaml2obj] Make e_phoff and e_phentsize 0 if there are no program headers
Summary: It says here that if there are no program headers than e_phoff should be 0, but currently it is always set after the header. GNU's readelf (but not llvm-readelf) complains about this: readelf: Warning: possibly corrupt ELF header - it has a non-zero program header offset, but no program headers.
Reviewers: jhenderson, grimar, MaskRay, rupprecht
Reviewed By: jhenderson, grimar, MaskRay
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D67054