IRGen: Remove different NoAlias behavior at Ounchecked

As per discussion on the mailing list we don't want different behavior for
programmer errors at Ounchecked than at O for errors that are not diagnosable.

Neither O nor Ounchecked will now emit LLVM's NoAlias attribute for inout
parameters.

rdar://20041458

Swift SVN r25784

lib/Frontend/CompilerInvocation.cpp

@@ -821,7 +821,6 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
     } else if (A->getOption().matches(OPT_Ounchecked)) {
       // Turn on optimizations and remove all runtime checks.
       IRGenOpts.Optimize = true;
-      IRGenOpts.Unchecked = true;
       // Removal of cond_fail (overflow on binary operations).
       Opts.RemoveRuntimeAsserts = true;
       Opts.AssertConfig = SILOptions::Fast;