The section headers present in the DBI stream got lost when using
`pdb2yaml` and `yaml2pdb`.
They are a list of COFF section headers. The
`llvm::object::coff_section` didn't have a YAML mapping, so I added one
in llvm-pdbutil. The mapping for COFF sections in ObjectYAML includes
the section data itself, so we can't use it here.
Creation of the section map and headers in yaml2pdb is done like in LLD:
438a18c1e1/lld/COFF/PDB.cpp (L1695-L1703)
d99c840d16