[PECOFF] Handle scope of absolute atom correctly.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@184035 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Support .lib archive file.

Archive file in Windows has file extension of ".lib" but the file format is
in fact the same as Unix. It's an ar archive holding multiple .obj files.
The existing archive reader can read .lib files.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@184036 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Add a test for r184036.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@184037 91177308-0d34-0410-b5e6-96231b3b80d8