Don't allow direct access to StreamString's internal buffer.

This is a large API change that removes the two functions from
StreamString that return a std::string& and a const std::string&,
and instead provide one function which returns a StringRef.

Direct access to the underlying buffer violates the concept of
a "stream" which is intended to provide forward only access,
and makes porting to llvm::raw_ostream more difficult in the
future.

Differential Revision: https://reviews.llvm.org/D26698

llvm-svn: 287152
diff --git a/lldb/source/Interpreter/Options.cpp b/lldb/source/Interpreter/Options.cpp
index c95876f..d26e53f 100644
--- a/lldb/source/Interpreter/Options.cpp
+++ b/lldb/source/Interpreter/Options.cpp
@@ -529,7 +529,7 @@
         if (cmd->WantsRawCommandString() && !only_print_args)
           strm.Printf(" --");
 
-        strm.Printf(" %s", args_str.GetData());
+        strm << " " << args_str.GetString();
         if (only_print_args)
           break;
       }
@@ -541,7 +541,7 @@
     if (!only_print_args)
       strm.PutChar('\n');
     strm.Indent(name);
-    strm.Printf(" %s", arguments_str.GetData());
+    strm << " " << arguments_str.GetString();
   }
 
   strm.Printf("\n\n");