Fixed build

src/config.hpp

@@ -324,7 +324,7 @@ public:
 			instances--;
 		}
 
-		static const bool do_throw()
+		static bool do_throw()
 		{
 			return instances > 0;
 		}

src/utils/optional_reference.hpp

@@ -56,7 +56,9 @@ public:
 		if(opt_) {
 			return opt_->get();
 		} else {
-			throw std::bad_optional_access{};
+			// We're going to drop this codepath once we can use optional::value anyway, but just
+			// noting we want this function to ultimately throw std::bad_optional_access.
+			throw std::runtime_error("Optional reference has no value");
 		}
 #endif
 	}