IRGen: support emitting specialized witness tables

lib/IRGen/IRGenModule.cpp

@@ -1381,6 +1381,10 @@ bool IRGenerator::canEmitWitnessTableLazily(SILWitnessTable *wt) {
   if (Opts.UseJIT)
     return false;
 
+  // witness tables are always emitted lazily in embedded swift.
+  if (SIL.getASTContext().LangOpts.hasFeature(Feature::Embedded))
+    return true;
+
   // Regardless of the access level, if the witness table is shared it means
   // we can safely not emit it. Every other module which needs it will generate
   // its own shared copy of it.