Previously, there is no way to create a stream other than pre-defined
special stream such as DBI or IPI. This patch adds a new method,
addDbgStream, to add a debug stream to a PDB file.
Differential Revision: https://reviews.llvm.org/D25356
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@283823 91177308-0d34-0410-b5e6-96231b3b80d8