Add a comment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186035 91177308-0d34-0410-b5e6-96231b3b80d8
Move tests from test/Archive to test/Object.

There is no lib/Archive anymore and some archive tests were in test/Archive and
others in test/Object. Since archive is just one of the formats supported by
lib/Object, test/Object is probably the best location.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186038 91177308-0d34-0410-b5e6-96231b3b80d8