[embedded] Make CMO's 'serialize everything' mode even more aggressive and allow serialization of private and shared functions

lib/Frontend/CompilerInvocation.cpp

@@ -3117,6 +3117,7 @@ bool CompilerInvocation::parseArgs(
   if (LangOpts.hasFeature(Feature::Embedded)) {
     IRGenOpts.InternalizeAtLink = true;
     IRGenOpts.DisableLegacyTypeInfo = true;
+    SILOpts.CMOMode = CrossModuleOptimizationMode::Everything;
   }
 
   return false;