[clang] add help text for constexpr step limit opt-out

Author: Tsche

clang/include/clang/Driver/Options.td

@@ -2045,7 +2045,7 @@ def fconstexpr_depth_EQ : Joined<["-"], "fconstexpr-depth=">, Group<f_Group>,
   MarshallingInfoInt<LangOpts<"ConstexprCallDepth">, "512">;
 def fconstexpr_steps_EQ : Joined<["-"], "fconstexpr-steps=">, Group<f_Group>,
   Visibility<[ClangOption, CC1Option]>,
-  HelpText<"Set the maximum number of steps in constexpr function evaluation">,
+  HelpText<"Set the maximum number of steps in constexpr function evaluation (0 = no limit)">,
   MarshallingInfoInt<LangOpts<"ConstexprStepLimit">, "1048576">;
 def fexperimental_new_constant_interpreter : Flag<["-"], "fexperimental-new-constant-interpreter">, Group<f_Group>,
   HelpText<"Enable the experimental new constant interpreter">,