Add a unit test for loading an object file via a file descriptor.  Patch by Pete Cooper.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197600 91177308-0d34-0410-b5e6-96231b3b80d8
Revert r197600 while I sort out why it's failing on Windows.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197602 91177308-0d34-0410-b5e6-96231b3b80d8