[PDB] Move PDB functions to a separate file.

We are going to use the hash functions from TPI streams.

Differential Revision: http://reviews.llvm.org/D21142

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272223 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed