[readobj] Expand CodeView dumping functionality

This rewrites and expands the existing codeview dumping functionality in
llvm-readobj using techniques similar to those in lib/Object. This defines a
number of new records and enums useful for reading memory mapped codeview
sections in COFF objects.

The dumper is intended as a testing tool for LLVM as it grows more codeview
output capabilities.

Reviewers: majnemer

Differential Revision: http://reviews.llvm.org/D16104

llvm-svn: 257658