readobj: Dump PE/COFF optional records.

These records are mandatory for executables and are used by the loader.

Reviewers: rafael

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D939

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183852 91177308-0d34-0410-b5e6-96231b3b80d8