Fix three build and link breaks in shared code

src/helpers/ConfigSerializer.cpp

@@ -1,5 +1,8 @@
 #include "ConfigSerializer.h"
 
+#include <stdlib.h>   // atoi/atol/atof -- reaches these via Arduino.h on MCU
+                      // targets, but not in the host `native` test build
+
 bool ConfigSerializer::saveSerial(Stream& s) {
   Context context(&s, OP::WRITE);
   _context = &context;  // set the context for structure() call

src/helpers/radiolib/CustomLLCC68Wrapper.h

@@ -35,7 +35,7 @@ class CustomLLCC68Wrapper : public RadioLibWrapper {
   }
   uint8_t getSpreadingFactor() const override { return ((CustomLLCC68 *)_radio)->spreadingFactor; }
 
-  void doResetAGC() override { sx126xResetAGC((SX126x *)_radio); }
+  void doResetAGC() override { sx126xResetAGC((SX126x *)_radio, getRxBoostedGainMode()); }
 
   bool setRxBoostedGainMode(bool en) override {
     return ((CustomLLCC68 *)_radio)->setRxBoostedGainMode(en) == RADIOLIB_ERR_NONE;

src/helpers/sensors/LocationProvider.h

@@ -16,7 +16,7 @@ class LocationProvider {
     virtual long satellitesCount() = 0;
     virtual bool isValid() = 0;
     virtual long getTimestamp() = 0;
-    virtual void sendSentence(const char * sentence);
+    virtual void sendSentence(const char * sentence) {}
     virtual void reset() = 0;
     virtual void begin() = 0;
     virtual void stop() = 0;