Remove now-unnecessary enum keyword (#1338)

C++ does not need it

src/asm/opt.cpp

@@ -28,7 +28,7 @@ struct OptStackEntry {
 	bool warnOnLdOpt;
 	bool warningsAreErrors;
 	size_t maxRecursionDepth;
-	enum WarningState warningStates[numWarningStates];
+	WarningState warningStates[numWarningStates];
 };
 
 static std::stack<OptStackEntry> stack;