Always use / as the path separator.

It is not clear if it is worth the complexity to use \ on
windows. This should fix the bots.

llvm-svn: 288616
diff --git a/llvm/tools/llvm-ar/llvm-ar.cpp b/llvm/tools/llvm-ar/llvm-ar.cpp
index 26f8d5b..b99a396 100644
--- a/llvm/tools/llvm-ar/llvm-ar.cpp
+++ b/llvm/tools/llvm-ar/llvm-ar.cpp
@@ -362,7 +362,7 @@
 
   if (C.getParent()->isThin()) {
     outs() << sys::path::parent_path(ArchiveName);
-    outs() << sys::path::get_separator();
+    outs() << '/';
   }
   outs() << Name << "\n";
 }