Eagerly update a protocol's "has missing required members" flag.

Rather than plumbing a "has missing required members" flag all the way
through the LazyResolver's loadAllMembers and its implementations,
just eagerly update the "has missing required members" flag in the
Clang importer when it happens. More NFC cleanup.

lib/Serialization/Deserialization.cpp

@@ -3919,9 +3919,7 @@ Type ModuleFile::getType(TypeID TID) {
   return typeOrOffset;
 }
 
-void ModuleFile::loadAllMembers(Decl *D,
-                                uint64_t contextData,
-                                bool *) {
+void ModuleFile::loadAllMembers(Decl *D, uint64_t contextData) {
   PrettyStackTraceDecl trace("loading members for", D);
 
   BCOffsetRAII restoreOffset(DeclTypeCursor);