[-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

llvm-svn: 188244