Add llvm-pdbdump to tools.

Add llvm-pdbdump to tools.

llvm-pdbdump is a tool which can be used to dump the contents
of Microsoft-generated PDB files.  It makes use of the Microsoft
DIA SDK, which is a COM based library designed specifically for
this purpose.

The initial commit of this tool dumps the raw bytes from PDB data
streams.  Future commits will dump more semantic information such
as types, symbols, source files, etc similar to the types of
information accessible via llvm-dwarfdump.

Reviewed by: Aaron Ballman, Reid Kleckner, Chandler Carruth
Differential Revision: http://reviews.llvm.org/D7153

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227241 91177308-0d34-0410-b5e6-96231b3b80d8