Path: Recognize COFF import library file magic.

Summary: Make identify_magic to recognize COFF import file.

Reviewers: Bigcheese

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D2165

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194852 91177308-0d34-0410-b5e6-96231b3b80d8