Fix OS default in Makefile.rules for Windows. http://reviews.llvm.org/D9043
Fix OS default in Makefile.rules for Windows. http://reviews.llvm.org/D9043

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@235056 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb