Improve llvm-pdbdump output display.

This patch adds a number of improvements to llvm-pdbdump.

1) Dumping of the entire global scope, and not only those
   symbols that live in individual compilands.
2) Prepend class name to member functions and data
3) Improved display of bitfields.
4) Support for dumping more kinds of data symbols.

llvm-svn: 229012