test: attempt to repair windows build
test: attempt to repair windows build

Replace use of /dev/null with /var/empty.  lit will substitute the /dev/null
include path resulting in failures.  Use a path under /var/empty which is
supposed to be empty to ensure that we can successfully test.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@268784 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang