XFAIL this test on mingw.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186444 91177308-0d34-0410-b5e6-96231b3b80d8
Finally, force the target for this test. Should unbreak non-x86 buildbots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186445 91177308-0d34-0410-b5e6-96231b3b80d8
Add a wrapper for open.

This centralizes the handling of O_BINARY and opens the way for hiding more
differences (like how open behaves with directories).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186447 91177308-0d34-0410-b5e6-96231b3b80d8