Print objects of specific classes better in JIT::Type::toString @override-unit-failures

Right now it returns "{}".

hphp/runtime/vm/jit/ir.cpp

@@ -55,6 +55,10 @@ std::string Type::toString() const {
   IR_TYPES
 # undef IRT
 
+  if (strictSubtypeOf(Type::Obj)) {
+    return folly::format("Obj<{}>", m_class->name()->data()).str();
+  }
+
   // Concat all of the primitive types in the custom union type
   std::vector<std::string> types;
 # define IRT(name, ...) if (name.subtypeOf(*this)) types.push_back(#name);