[Object/COFF] Add dos_header, pe32{,plus}_header and data_directory.

Reviewers: Bigcheese

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D905

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183087 91177308-0d34-0410-b5e6-96231b3b80d8