Teach raw_ostream to accept SmallString.

Saves adding .str() call to any raw_ostream << SmallString usage
and a small step towards making .str() consistent in the ADTs by
removing one of the SmallString::str() use cases, discussion at

http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20141013/240026.html

I'll update the Phabricator patch http://reviews.llvm.org/D6372
for review of the Twine SmallString support, it's more complex
than this one.

llvm-svn: 231763
diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index b2a1b24..140cdd8 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -1034,7 +1034,7 @@
     Str += llvm::utostr(AnonStructId);
 
     Out << Str.size();
-    Out << Str.str();
+    Out << Str;
     break;
   }