work around old GCC bug

Author: vmatare

src/driver.h

@@ -31,7 +31,9 @@ namespace thinkfan {
 class Driver {
 protected:
 	Driver(bool optional, unsigned int max_errors);
-	virtual ~Driver() noexcept(false) = default;
+
+	virtual ~Driver() noexcept(false)
+	{}
 
 	template<typename FnSignatureT>
 	using FN = std::function<FnSignatureT>;