Read the rest of the DBI substreams, and parse source info.

We now read out the rest of the substreams from the DBI streams.  One of
these substreams, the FileInfo substream, contains information about which
source files contribute to each module (aka compiland).  This patch
additionally parses out the file information from that substream, and
dumps it in llvm-pdbdump.

Differential Revision: http://reviews.llvm.org/D19634
Reviewed by: ruiu

llvm-svn: 267928