[llvm-pdbdump] Many minor fixes and improvements

A short list of some of the improvements:

1) Now supports -all command line argument, which implies many
   other command line arguments to simplify usage.
2) Now supports -no-compiler-generated command line argument to
   exclude compiler generated types.
3) Prints base class list.
4) -class-definitions implies -types.
5) Proper display of bitfields.
6) Can now distinguish between struct/class/interface/union.

And a few other minor tweaks.

llvm-svn: 230933