[Serialization] Handle llvm::Error in member deserialization recovery (#16957)

llvm::Expected/llvm::Error require that the error is not just checked
but explicitly handled. Since we're currently recovering as if nothing
happened, we need to use llvm::consumeError to throw the error info
away.

rdar://problem/40738521

lib/Serialization/ModuleFile.cpp

@@ -1860,6 +1860,8 @@ ModuleFile::loadNamedMembers(const IterableDeclContext *IDC, DeclBaseName N,
       } else {
         if (!getContext().LangOpts.EnableDeserializationRecovery)
           fatal(mem.takeError());
+        llvm::consumeError(mem.takeError());
+
         // Treat this as a cache-miss to the caller and let them attempt
         // to refill through the normal loadAllMembers() path.
         return None;