[llvm-cov] Attempt to appease Windows bots

They appear to reject r275640 because stdin is held open during an
ExecuteAndWait in which it's redirected:

  http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast/builds/8390

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275642 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed