Serialization: Switch over to using the native SmallVector based BitstreamWriter
ctor.

llvm-svn: 151752
diff --git a/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp b/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp
index 7a8edf7..7bf8742 100644
--- a/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp
+++ b/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp
@@ -159,7 +159,7 @@
   const DiagnosticOptions &DiagOpts;
   
   /// \brief The byte buffer for the serialized content.
-  std::vector<unsigned char> Buffer;
+  SmallString<1024> Buffer;
 
   /// \brief The BitStreamWriter for the serialized diagnostics.
   llvm::BitstreamWriter Stream;