`file` is not available on windows except through GnuWin32, and that
`file` was identifying the ClangModule as an ACB Archive file instead of
a COFF file.
Instead of using `file`, it is easier and more portable to use
llvm-readobj. I also converted the egrep usage into FileCheck while
adding COFF support.
1. Require objc_interop (the Linux bot currently fails to import
Objective-C modules.
2. Generalize the testcase to also accept ELF containers so it works when
(1) is resolved.
Swift SVN r28630