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

@@ -1575,7 +1575,7 @@ 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;
     }

test/embedded/wmo-with-embedded-diag.swift

@@ -1,8 +1,8 @@
 // RUN: %target-swift-frontend -typecheck -parse-stdlib %s -enable-experimental-feature Embedded
 // RUN: not %target-swift-frontend -typecheck -parse-stdlib %s -primary-file %s -enable-experimental-feature Embedded 2>&1 | %FileCheck %s
 
-// RUN: %target-swiftc_driver -typecheck -parse-stdlib %s -Xfrontend -disable-objc-interop -enable-experimental-feature Embedded -wmo
-// RUN: not %target-swiftc_driver -typecheck -parse-stdlib %s -Xfrontend -disable-objc-interop -enable-experimental-feature Embedded 2>&1 | %FileCheck %s
+// RUN: %target-swiftc_driver -c %s -o %t -parse-stdlib -Xfrontend -disable-objc-interop -enable-experimental-feature Embedded -wmo
+// RUN: not %target-swiftc_driver -c %s -o %t -parse-stdlib -Xfrontend -disable-objc-interop -enable-experimental-feature Embedded 2>&1 | %FileCheck %s
 
 // REQUIRES: swift_in_compiler