[Serialization] Skip verifying attributes when allowing errors

When allowing errors any attribute could be on any decl, so don't verify
whether an attribute can appear on a decl. Note that these attributes
aren't serialized anyway since they'll be set to invalid during
typechecking and hence skipped.

lib/Serialization/Serialization.cpp

@@ -2012,6 +2012,8 @@ getStableSelfAccessKind(swift::SelfAccessKind MM) {
 # define DECL(KIND, PARENT)\
 LLVM_ATTRIBUTE_UNUSED \
 static void verifyAttrSerializable(const KIND ## Decl *D) {\
+  if (D->Decl::getASTContext().LangOpts.AllowModuleWithCompilerErrors)\
+    return;\
   for (auto Attr : D->getAttrs()) {\
     assert(Attr->canAppearOnDecl(D) && "attribute cannot appear on a " #KIND);\
   }\