[pdb] Round-trip module & file info to/from YAML.

[pdb] Round-trip module & file info to/from YAML.

This implements support for writing compiland and compiland source
file info to a binary PDB.  This is tested by adding support for
dumping these fields from an existing PDB to yaml, reading them
back in, and dumping them again and verifying the values are as
expected.

llvm-svn: 276426