RequirementMachine: Enable -requirement-machine-protocol-signatures=verify by default

Author: slavapestov

lib/Frontend/CompilerInvocation.cpp

@@ -876,6 +876,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.DisableSubstSILFunctionTypes =
       Args.hasArg(OPT_disable_subst_sil_function_types);
 
+  Opts.RequirementMachineProtocolSignatures = RequirementMachineMode::Verify;
+
   if (auto A = Args.getLastArg(OPT_requirement_machine_protocol_signatures_EQ)) {
     auto value = llvm::StringSwitch<Optional<RequirementMachineMode>>(A->getValue())
         .Case("off", RequirementMachineMode::Disabled)