Avoid enabling loaded module verification after WMO until playgrounds is fixed.

playground_lvalues.swift:
use of unresolved identifier '$builtin_log_with_id'

Additional verification could expose this problem elsewhere. It will be enable
on master later, but not as part of this PR.

Author: atrick

lib/Sema/TypeChecker.cpp

@@ -707,11 +707,16 @@ void swift::performWholeModuleTypeChecking(SourceFile &SF) {
   // been type checked. This avoids caching imported declarations when a valid
   // type checker is not present. The same declaration may need to be fully
   // imported by subsequent files.
+  //
+  // FIXME: some playgrounds tests (playground_lvalues.swift) fail with
+  // verification enabled.
+#if 0
   if (SF.Kind != SourceFileKind::REPL &&
       SF.Kind != SourceFileKind::SIL &&
       !Ctx.LangOpts.DebuggerSupport) {
     Ctx.verifyAllLoadedModules();
   }
+#endif
 }
 
 bool swift::performTypeLocChecking(ASTContext &Ctx, TypeLoc &T,