Directly determine if experimental feature active.

libsolidity/analysis/TypeChecker.h

@@ -165,6 +165,9 @@ private:
 	/// Runs type checks on @a _expression to infer its type and then checks that it is an LValue.
 	void requireLValue(Expression const& _expression, bool _ordinaryAssignment);
 
+	bool experimentalFeatureActive(ExperimentalFeature _feature) const;
+
+	SourceUnit const* m_currentSourceUnit = nullptr;
 	ContractDefinition const* m_currentContract = nullptr;
 
 	langutil::EVMVersion m_evmVersion;