Allow enabling embedded Swift without WMO when not generating SIL

This allows modes like -index-file to work the same way they do when not using embedded Swift

Author: owenv

lib/Frontend/CompilerInvocation.cpp

@@ -1379,7 +1379,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
       HadError = true;
     }
 
-    if (!FrontendOpts.InputsAndOutputs.isWholeModule()) {
+    if (!FrontendOpts.InputsAndOutputs.isWholeModule() && FrontendOptions::doesActionGenerateSIL(FrontendOpts.RequestedAction)) {
       Diags.diagnose(SourceLoc(), diag::wmo_with_embedded);
       HadError = true;
     }