[llvm-pdbdump] Add basic symbol dumping.

[llvm-pdbdump] Add basic symbol dumping.

This adds two command line options:

--symbols dumps a list of all symbols found in the PDB.
--symbol-details dumps the same list, but with detailed information
                 for every symbol such as type, attributes, etc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227286 91177308-0d34-0410-b5e6-96231b3b80d8