Add a flag (false by default) for large loadable types pass

lib/Frontend/CompilerInvocation.cpp

@@ -1378,6 +1378,7 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
     |= Args.hasArg(OPT_assume_parsing_unqualified_ownership_sil);
   Opts.EnableMandatorySemanticARCOpts |=
       !Args.hasArg(OPT_disable_mandatory_semantic_arc_opts);
+  Opts.EnableLargeLoadableTypes |= Args.hasArg(OPT_enable_large_loadable_types);
 
   if (Args.hasArg(OPT_debug_on_sil)) {
     // Derive the name of the SIL file for debugging from