Experiment: C++17 support (#9874)

* Add C++17 support

* Add C++17 runtime probes and update build configurations for STM32 and Portduino

* Remove unflags

* Update C++ standard flags across the platforms

* Convert a couple of instances to structured bindings

* NRF52 platform.txt to add C++17 support

* Still need the unflags apparently

* Remove C++17 runtime probe tests from test_main.cpp

* Reconfigured doesnt need a nodiscard

* Remove nodiscard attribute from init() method in RadioInterface

* Remove mbedtls/error.h from build flags

Removed include directive for mbedtls/error.h from build flags.

* Fix IRAM overflow

* Fix IRAM overflow

* Add build flag to exclude MQTT from rak11200

* Update C++ standard from gnu17 to gnu++17

src/mesh/NextHopRouter.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "FloodingRouter.h"
+#include <optional>
 #include <unordered_map>
 
 /**
@@ -146,7 +147,7 @@ class NextHopRouter : public FloodingRouter
      * Get the next hop for a destination, given the relay node
      * @return the node number of the next hop, 0 if no preference (fallback to FloodingRouter)
      */
-    uint8_t getNextHop(NodeNum to, uint8_t relay_node);
+    std::optional<uint8_t> getNextHop(NodeNum to, uint8_t relay_node);
 
     /** Check if we should be rebroadcasting this packet if so, do so.
      *  @return true if we did rebroadcast */