Add "rust-enabled" to --version output

This adds "rust-enabled" to the --version output, so it's easier to
tell if lldb has rust support.

Author: tromey

lldb/source/lldb.cpp

@@ -73,5 +73,9 @@ const char *lldb_private::GetVersion() {
       g_version_str += llvm_rev;
     }
   }
+
+  // We don't have a version number (yet?).
+  g_version_str += "\n  rust-enabled";
+
   return g_version_str.c_str();
 }