Don't use <sstream> in Streams.h but <iosfwd> instead.

llvm-svn: 32340
diff --git a/llvm/lib/Support/PluginLoader.cpp b/llvm/lib/Support/PluginLoader.cpp
index 97b253e..3c9de89 100644
--- a/llvm/lib/Support/PluginLoader.cpp
+++ b/llvm/lib/Support/PluginLoader.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Support/PluginLoader.h"
 #include "llvm/Support/Streams.h"
 #include "llvm/System/DynamicLibrary.h"
+#include <ostream>
 #include <vector>
 using namespace llvm;