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

llvm-svn: 32340
diff --git a/llvm/lib/VMCore/Verifier.cpp b/llvm/lib/VMCore/Verifier.cpp
index cf812a8..2b9bb6b 100644
--- a/llvm/lib/VMCore/Verifier.cpp
+++ b/llvm/lib/VMCore/Verifier.cpp
@@ -60,6 +60,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Compiler.h"
 #include <algorithm>
+#include <sstream>
 #include <cstdarg>
 using namespace llvm;