Update GenerateAdditionalHelpAvenues to take StringRef.

llvm-svn: 287155
diff --git a/lldb/source/Commands/CommandObjectHelp.h b/lldb/source/Commands/CommandObjectHelp.h
index 5e3cf74..721917a 100644
--- a/lldb/source/Commands/CommandObjectHelp.h
+++ b/lldb/source/Commands/CommandObjectHelp.h
@@ -35,8 +35,8 @@
                        StringList &matches) override;
 
   static void GenerateAdditionalHelpAvenuesMessage(
-      Stream *s, const char *command, const char *prefix = nullptr,
-      const char *subcommand = nullptr, bool include_apropos = true,
+      Stream *s, llvm::StringRef command, llvm::StringRef prefix,
+      llvm::StringRef subcommand, bool include_apropos = true,
       bool include_type_lookup = true);
 
   class CommandOptions : public Options {