[func-sig-opts] Add frontend option -enable-func-sig-opts to enable function signature optimization as a late pass. This is disabled by default and is only for testing purposes.

Swift SVN r21787

lib/Frontend/CompilerInvocation.cpp

@@ -826,6 +826,7 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
   Opts.TimeTransforms |= Args.hasArg(OPT_sil_time_transforms);
   Opts.DebugSerialization |= Args.hasArg(OPT_sil_debug_serialization);
   Opts.PrintInstCounts |= Args.hasArg(OPT_print_inst_counts);
+  Opts.EnableFuncSigOpts |= Args.hasArg(OPT_enable_func_sig_opts);
 
   return false;
 }