Add the start of DIE hashing for DWARF4 type units and split dwarf
CUs.

Currently only hashes the name of CUs and the names of any children,
but it's an obvious first step to show the framework. The testcase
should continue to be correct, however, as it's an empty TU.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188243 91177308-0d34-0410-b5e6-96231b3b80d8
[-cxx-abi microsoft] Stick zero initialized symbols into the .bss section for COFF

Summary:
We need to do two things:

- Initialize BSSSection in MCObjectFileInfo::InitCOFFMCObjectFileInfo
- Teach TargetLoweringObjectFileCOFF::SelectSectionForGlobal what to do
  with it

This fixes PR16861.

Reviewers: rnk

Reviewed By: rnk

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1361

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188244 91177308-0d34-0410-b5e6-96231b3b80d8