PR14581: Make SourceLocation::printToString work, or it will always return an empty string.

No test case, this is debugging code.

llvm-svn: 169980
diff --git a/clang/lib/Basic/SourceLocation.cpp b/clang/lib/Basic/SourceLocation.cpp
index 0d62f7b..1822091 100644
--- a/clang/lib/Basic/SourceLocation.cpp
+++ b/clang/lib/Basic/SourceLocation.cpp
@@ -65,7 +65,7 @@
   std::string S;
   llvm::raw_string_ostream OS(S);
   print(OS, SM);
-  return S;
+  return OS.str();
 }
 
 void SourceLocation::dump(const SourceManager &SM) const {