[silgen] Add support for emitting guaranteed self behind the flag -enable-guaranteed-self.

This does not have any tests since I am going to start going through SILGen
tests and updating them for guaranteed self as the appropriate tests.

*NOTE* There is more work to be done in terms of thunks, but the basic
functionality is done.

rdar://15729033

Swift SVN r23653

lib/Frontend/CompilerInvocation.cpp

@@ -865,6 +865,7 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
   Opts.DebugSerialization |= Args.hasArg(OPT_sil_debug_serialization);
   Opts.PrintInstCounts |= Args.hasArg(OPT_print_inst_counts);
   Opts.EnableFuncSigOpts &= !Args.hasArg(OPT_disable_func_sig_opts);
+  Opts.EnableGuaranteedSelf |= Args.hasArg(OPT_enable_guaranteed_self);
 
   return false;
 }